feat: Add experimental sqlite-fts skeleton and subset HTTP Server (not C3)

[guozhihao-224]

Summary

• Add a TypeScript-owned node:sqlite persistence skeleton (Analyzer v1 FTS, experimental schema stamp, remember/list/get/search) so language-switch pits can be probed on self-created databases.
• Add a narrowed Fastify subset Server that composes that runtime and serves health, capabilities, and Memory over the pinned OpenAPI validators, using @powercontext/client in-process.
• Keep claims honest: PACKAGE_PROFILE stays sqlite-fts as the intended M2 line, EXPERIMENTAL_SUBSET is true, capture stays 503, search score is a placeholder, and docs/user/README.md still says HTTP Server is not shipped.

This is not shared-database C3, not a Python replacement, and does not follow Python main.

Profile and parity

• Profile: experimental sqlite-fts subset (not a sqlite-fts / C3 claim)
• Target level: C0 composition + C1 wire for registered routes only
• Related issue or RFC: Subset Server and cross-language HTTP E2E #5 (narrowed; subset HTTP on TS-created DBs). ADR 0008 (unavailable, no fake success), ADR 0002 (no powercontext.database.v1 writes)
• Does not close SQLite kernel and schema-version gate #3 or Memory, FTS, and PreparedContext #4

Checklist

• Does not add a second wire contract
• Does not hand-edit contract/ or conformance/ snapshots
• Does not hand-edit packages/protocol/src/generated
• Baseline bump, if any, is this pull request’s only purpose (no bump)
• New or changed behavior names the compatibility decision or ADR

Test plan

• pnpm format:write
• pnpm lint
• pnpm typecheck
• pnpm build
• pnpm test
• pnpm generate:check
• Server tests: CJK remember → close → listen same DB still searches; vector/hybrid 503; capture 503; unregistered work route 404; source_refs wire uses { name, source_id }