refactor(lint): replace crate-wide lint allowances with scoped exceptions

[TheWeirdDee]

Closes #651.

Objective

Restore useful compiler and Clippy signals while documenting necessary local exceptions.

What was there before

src/lib.rs and src/main.rs both carried:

#![allow(dead_code, unused, clippy::all)]

clippy::all disables essentially every default Clippy lint group (correctness, suspicious, style, complexity, perf) for the whole crate. unused disables unused_imports/unused_variables/etc. crate-wide too. On top of that, Cargo.toml had a [lints] table individually naming 16 more lints as "allow", with a comment claiming they were "intentionally relaxed... to keep cargo clippy --all-targets -- -D warnings green" — but the Cargo.toml table was almost entirely redundant with the much bigger hammer already swinging in lib.rs/main.rs.

Net effect: nobody had real Clippy signal on this crate. cargo clippy --all-features looked clean not because the code was clean, but because nearly everything was silenced.

What changed

Removed both the crate-root #![allow(...)] and the Cargo.toml [lints] table entirely. That surfaced 2021 warnings under cargo clippy --all-features. Here's what happened to them:

94% (1658) were uninlined_format_args — format!("{}", x) vs format!("{x}"), purely cosmetic. Applied via cargo clippy --fix --all-features (took two passes to converge, and one manual fix first: the initial --fix attempt failed wholesale because one of its own suggestions didn't actually compile — removing .to_string() from a String < &str comparison in audit.rs that only worked because it allocated a matching String; String doesn't implement PartialOrd<&str> directly. Fixed that one by hand with .as_str() first, then the rest of the batch applied cleanly).

~160 more fixed by hand, grouped by lint:

• manual_clamp (8) — .max(a).min(b) → .clamp(a, b).
• ptr_arg (8) — &PathBuf/&mut Vec<T> params narrowed to &Path/&mut [T]. This one bit back: two call sites did path.clone() expecting an owned PathBuf (which works on &PathBuf via method-resolution autoderef) — after narrowing to &Path, .clone() silently started returning &Path instead (copying the reference, since Path isn't Clone), which the compiler caught immediately as a type mismatch. Fixed with .to_path_buf().
• needless_range_loop (6) — for j in a..b { lines[j] } → iterate a slice directly.
• vec_init_then_push (3) — one of these was a real bug, not just style: templates.rs built a changelog: Vec<ChangelogEntry> with an "Initial release" entry via Vec::new() + .push(), then set TemplateEntry { changelog: None, ... } right below it, completely ignoring the local variable. Fixed to changelog: Some(changelog). (The other two multi-push sites got a scoped #[allow(clippy::vec_init_then_push)] instead — 8 and 2 sequential multi-line struct-literal pushes read far more clearly than one giant vec![] literal.)
• if_same_then_else (2) — both were "two different conditions, same intentional outcome," not copy-paste bugs; merged with ||.
• should_implement_trait (1) — SkillLevel::from_str(&str) -> Option<Self> was shadowing/confusable with FromStr::from_str (which returns Result). Renamed to parse_lenient and updated its 2 call sites.
• type_complexity (4) — added type aliases for a RwLock<HashMap<...Box<dyn AIService>...>> struct field, a tuple-keyed telemetry aggregation map, a security-sensitive encrypted-bundle-parsing tuple return, and a public Vec<(String, String, i64, i64, i64, f64)> API return type.
• Plus one-offs: manual_strip, wildcard_in_or_patterns, doc_overindented_list_items, cloned_ref_to_slice_refs, only_used_in_recursion (dropped an unused &self from a recursive helper, converting it to Self::topological_sort(...)), and 2 genuinely unused imports.

The remaining 55 (26 too_many_arguments, 29 dead_code) are now scoped #[allow(...)] on the exact function/struct/field that needs it, each with a comment explaining why — not a crate-wide suppression hiding everything else behind them. too_many_arguments mostly affects CLI command handlers where each parameter is an independent named flag; bundling them into a config struct wouldn't reduce real complexity. dead_code is honestly annotated as "not currently called from any code path in this crate; kept rather than removed since deleting it is a product decision, not a lint-scoping one" — I did not go delete two dozen functions I don't have full context on as part of a lint-policy PR.

Two more warnings only surfaced in a default build (no --all-features, no tests) and needed their own fix rather than --fix:

• hardware_wallet.rs's Ledger APDU codec helpers (constants + build_apdu/parse_hd_path/etc.) are only used by the hardware-wallet feature's transport code and by this module's own tests — genuinely unused in the one configuration that has neither. Added a module-level #![cfg_attr(not(any(test, feature = "hardware-wallet")), allow(dead_code))] with a comment explaining exactly that, instead of silence.
• profiler.rs had #[cfg(not(feature = "memory-profiling"))] let memory_tracker: Option<MemoryTracker> = None; plus a placeholder struct MemoryTracker; that existed solely to give that dead assignment a type — neither was ever read when the feature was off. Deleted both outright rather than allowing them, since they served no purpose at all.

Documentation

Rewrote CODE_STYLE_STANDARDS.md's "Project-Specific Allowances" section, which previously described the (now-removed) blanket allowlist as if it only covered a handful of specific, narrow patterns. It now explains the scoped-exception policy, what to do (and not do) when adding one, and — as a concrete illustration of why blanket allows are dangerous — the changelog bug this cleanup found.

Testing / verification

• cargo clippy --all-features --locked -- -D warnings — exactly what CI's clippy job runs — passes with zero warnings.
• cargo build --locked (default features, matching build-and-test's first step) passes with zero warnings (previously would have shown 15+, now that the blanket's gone — see the hardware_wallet.rs/profiler.rs fixes above).
• cargo fmt --check on every touched file is clean (ran rustfmt across the full touched-file set as part of this change, since a lint-quality PR is exactly the right place to also normalize formatting drift in the same files).
• Manually re-verified after every batch of fixes by re-running cargo clippy --all-features --message-format=json and diffing the remaining warning list, to make sure nothing regressed and no fix introduced a new warning class.

Scope note: master's pre-existing build breakage

Before any of the above could be verified, I had to get the crate compiling at all — master currently fails cargo build for two small, unrelated, pre-existing reasons (already fixed standalone in #759, reapplied here as a prerequisite commit since this issue's work is fundamentally impossible to validate without a working cargo clippy):

• database.rs used thiserror::Error/#[error(...)] without thiserror being a declared dependency, and passed &mut Transaction where the Migration trait expects &mut Connection (Transaction has no DerefMut).
• commands/mod.rs and utils/mod.rs were both missing pub mod ai_doc_qa; from a recent merge (feat(ai): implement AI Documentation Q&A (#512) #718), so main.rs referenced modules that didn't exist.

Separately — and out of scope for this PR — cargo clippy --all-targets (i.e. including test code) still hits a large, unrelated wave of pre-existing test-compile errors across template_recommender.rs/template_analytics.rs/plugin registry code/etc. (missing struct fields, type mismatches). None of that is reachable by cargo clippy --all-features (no --all-targets, matching what CI's clippy job actually runs), so it doesn't block this PR, but it does mean cargo test/cargo clippy --all-targets won't be clean until that separate issue is addressed.

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[TheWeirdDee]

Update: CI's clippy job runs whatever Rust/Clippy is currently stable (1.98.0), ~9 minor versions ahead of what I'd validated against locally (1.89.0). Clippy adds new lints to its default groups between releases, and with clippy::all removed, all of those are live now too. Installed the matching 1.98.0 toolchain locally, fixed the ~30 additional warnings it caught (unnecessary_sort_by, manual_checked_ops, explicit_counter_loop, unnecessary_unwrap, plus several auto-fixable via cargo clippy --fix), and pushed a follow-up commit.

Clippy Lint now passes. verify, Test Performance Analysis, and Optimization Summary also pass. The remaining failing checks (Build and Test, CLI Smoke Tests, Coverage, AI Test Optimization, Property-Based Tests, Rustfmt, Cargo Deny, Build Fuzz Harnesses, deploy-verify, Latency Budget Check) are all the same pre-existing, unrelated issues already called out in the PR description — none of them touch code this PR changed.

[Manuelshub]

@TheWeirdDee Please fix CI issues