docs: focus README on safe cache rollouts

[lan17]

Summary

• replace the 10,916-word single-page README on current main with a 2,790-word adoption guide that identifies DialCache as a TypeScript read-through caching library before explaining its production and high-scale patterns
• explain the 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
• make the ownership boundary explicit: DialCache is an application library, not a frontend cache, cache server, Redis client, or configuration control plane
• provide a copyable local-only quick start, then reset every shared and shadow ramp to zero before production exposure; add metrics and runtime policy, connect Redis or Valkey without serving it, optionally validate tracked keys in shadow mode, and increase stable cohorts independently
• keep the README concise while moving complete configuration, Redis/Valkey, shadow validation, invalidation, coalescing/liveness, observability, and release contracts into seven focused reference guides
• use absolute GitHub file URLs for every README-to-repository link so the packaged 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 current v0.14.1

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 add, 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 introduces request coalescing, runtime policy, deterministic ramp-up and ramp-down, fail-open reads, non-serving Redis shadow validation and bootstrap, targeted invalidation, deadlines, serialization, and backend-neutral observability.

v0.14.1 refresh

This branch includes current main at v0.14.1 and documents the latest released contracts:

• root-exported ShadowConfig and grouped shadow: { ramp, logMismatches } policy, including independent sparse-leaf overlays, the complete kill switch, strict validation, and rejection of the removed shadowRamp field
• default-off, confirmed-only shadow mismatch warnings, including metric admission, exact fields, byte caps, native-JSON behavior, observer isolation, and the privacy and synchronous-work limits that truncation does not solve
• invalidateRemote() as an explicit Redis maintenance operation that rejects when Redis is absent instead of reporting a false success, while preserving bounded metrics, warning, validation order, and original-error propagation
• updated packed-export, Redis adapter, observability, compatibility, and maintainer guidance for the v0.14.1 surface

Impact

This is documentation-only relative to current main at v0.14.1.

Merging this PR does not republish v0.14.1; 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 — strict typecheck, 407 unit tests with coverage, builds/declarations, and packed ESM/CJS consumers
• corepack pnpm test:integration — 93 Redis, Valkey, and Redis Cluster tests
• corepack pnpm benchmark:request-local — all ten semantic scenarios passed
• fresh GitHub CI passed: package tests, both CodeQL analyses, and PR-title validation
• two-round independent editorial, technical, coverage, npm-consumer, and source-accuracy review; round one findings were fixed and the fresh confirmation round returned clean
• syntax-checked all 25 TypeScript documentation blocks
• validated 73 Markdown links plus three badge image URLs; every local file and anchor resolves
• README contains 21 absolute repository-file links and zero relative repository-file links
• longest non-list prose paragraph across the README and guides is 54 words
• git diff --check