docs: focus README on safe cache rollouts

[lan17]

Summary

• replace the 7,680-word single-page README with a 2,161-word backend adoption guide that first identifies DialCache as a TypeScript read-through caching library, then explains the production and high-scale patterns it adds around that core path
• explain the concrete execution model up front: wrap reusable readers with cached() or use getOrLoad() inline; after active layers miss, DialCache calls the application loader and publishes to active request-local, bounded process-local, and optional Redis or Valkey layers
• provide a copyable local-only quick start, then a safe production path that adds metrics, a remote TTL with a zero ramp, Redis or Valkey, and deterministic cohort expansion in that order
• make missing runtime policy fail safe in the rollout example by keeping both baseline ramps at zero
• clarify long-lived instance ownership, explicit enable/disable scopes, fail-open cache behavior, ramp-down semantics, value identity, invalidation boundaries, deadlines, and application-owned resource budgets
• move complete configuration, Redis/Valkey, serialization, invalidation, coalescing/liveness, observability, and release contracts into focused reference guides
• document the full custom Redis and metrics adapter contracts, advanced wire protocol, provider key input, lower-level context API, and compatibility-sensitive maintainer checks
• use absolute GitHub file URLs for every README-to-repository link so the README renders predictably on npm even though docs/ is not included in the package tarball
• preserve the Node.js 22.0.0 minimum and supported-LTS recommendation from v0.11.0

Why

The README on current main is technically thorough but makes experienced backend engineers work too hard to establish the basic mental model: What kind of cache is this? What happens on a miss? Which layers does it manage? Which production patterns does it provide, and which infrastructure and safety decisions remain application-owned?

The revised README answers those questions before setup. It frames DialCache as read-through caching first, then identifies the production patterns around it: request coalescing, runtime policy, deterministic ramp-up and ramp-down, fail-open reads, targeted invalidation, serialization, deadlines, and backend-neutral metrics. The quick start demonstrates a visible process-local hit, and the production path makes monitored remote rollout explicit.

Impact

This is documentation-only. The branch is based on current main at v0.11.0, including the Node.js >=22.0.0 runtime floor and dependency-advisory remediation.

Merging this PR does not republish v0.11.0; the rewritten README will appear on npm with a future package release. Its absolute links will resolve to the merged reference guides on main.

Validation

• corepack pnpm check under Node 22.22.0 — typecheck, 278 unit tests, coverage, builds/declarations, and packed consumers
• corepack pnpm test:integration — 73 Redis, Valkey, and Redis Cluster tests
• corepack pnpm benchmark:request-local — all six semantic scenarios passed, including one-read/one-timer deadline coalescing
• latest GitHub CI passed, including development/integration checks, the exact Node 22.0.0 packed-package floor, CodeQL, and PR-title validation
• three iterative editorial rounds across writing/engagement, onboarding safety, and reference accuracy; the final full round returned no findings
• final experienced-engineer explanation pass checks the opening in this order: category, execution model, cache layers, production patterns, rollout meaning, and ownership boundary
• syntax-checked all 23 TypeScript documentation blocks
• validated 49 Markdown links; all local files and anchors resolve
• README contains 18 absolute repository-file links and zero relative repository-file links
• longest prose paragraph across the README and guides is 54 words
• git diff --check