docs: focus README on safe cache rollouts

[lan17]

Summary

• replace the 10,397-word single-page README on current main with a 2,535-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 followed by a safe production path: add metrics, define a remote TTL with serving and shadow ramps at zero, connect Redis or Valkey, optionally validate tracked keys in shadow mode, then increase a stable serving cohort
• keep the README concise while moving complete configuration, Redis/Valkey, shadow validation, invalidation, coalescing/liveness, observability, and release contracts into 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 v0.13.0

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 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.

v0.13.0 refresh

This branch now includes current main and documents the contracts added in v0.12.0 and v0.13.0:

• one-year cache-TTL and invalidation-buffer ceilings, plus strict runtime ramp validation with no clamping
• shadowRamp, shadowMaxInFlight, shadowComparator, independent serving/shadow cohorts, and complete kill-switch semantics
• tracked Redis serving-hit validation and ramped-down clean-miss filling, including the C0 / source / C1 confirmation model
• capacity, deduplication, deadlines, detachment, shutdown, serializer, payload-ownership, invalidation-race, and command-amplification contracts
• Prometheus and Datadog shadow metrics, remote_shadow, all bounded outcomes, and observer rejection isolation
• updated coalescing, Redis lifecycle, invalidation-window, compatibility, and ten-scenario benchmark guidance

Impact

This is documentation-only relative to current main at v0.13.0.

Merging this PR does not republish v0.13.0; 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 — strict typecheck, 384 unit tests with coverage, builds/declarations, and packed 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: test, CodeQL, and PR-title validation
• independent iterative editorial and technical reviews across the README, maintainer map, core reference guides, and Redis/shadow guide; the final round returned no findings
• syntax-checked all 24 TypeScript documentation blocks
• validated 70 Markdown links; every local file and anchor resolves
• README contains 21 absolute repository-file links and zero relative repository-file links
• longest prose paragraph across the README and guides is 54 words
• git diff --check