Add a bounded client-side guest runtime

[keys-i]

Motivation

Provide an honest browser-native guest path without claiming complete Linux, BSD, ISA, or raw-socket compatibility.

Changes

• add bounded ELF64 loading, x86-64/AArch64 instruction subsets, and a hot-block WebAssembly JIT
• add Linux and FreeBSD syscall maps over bounded memory and virtual files
• harden BlockFS/OPFS persistence, mapping/file/output limits, and cooperative cancellation
• add deny-by-default Fetch/WebSocket transport and trusted host capability hooks for AI, Python, and Go runtimes
• add an optional injected v86 lifecycle adapter for higher-fidelity x86 PC images
• document exact instruction/syscall contracts, security limits, architecture, benchmarks, and a CSP-constrained playground

Verification

• npm run build — PASS; 71,745 B JavaScript and 3,842 B Wasm
• npm run validate — PASS; Biome, JavaScript regressions, and cargo test
• npm run benchmark — PASS; 80,219 simple ops/s, 64,874 parse ops/s, 239.7% warm Wasm improvement, 76.59x x86 and 84.84x AArch64 loop JIT speedups
• npm pack --dry-run — PASS; 71 files
• git diff --check — PASS
• browser execution — UNVERIFIED locally because Chromium, Firefox, chromedriver, and geckodriver are unavailable; CI owns that gate
• final gate — PASS via the documented gpt-5.6-sol fallback after the fixed gpt-5.6 gatekeeper model was unavailable for this account

Risks

This remains a documented instruction/syscall subset, not a distribution boot environment. Browser WebSockets may include ambient cookies, raw TCP/UDP requires a relay, mprotect does not enforce page permissions, and v86/source URLs remain host policy.

Rollback

Revert bed3189.

Closes #20
Closes #21
Refs #22
Refs #23
Refs #24
Refs #5