feat: establish peer database runtime contract

[xiaoland]

Summary

• define a provider-neutral inkcre database protocol with explicit peer roles, ACLs, default privileges, and a hard-cut migration that preserves production rows
• add idempotent lifecycle, deterministic development seed/reset, JSON readiness, canonical JWT validation, and digest-pinned local PostgREST
• prove the fresh pgvector/PostgREST chain in CI, publish immutable GHCR artifacts from main, and prepare guarded Eco production delivery for core + PostgREST

Verification

• pdm run check (123 passed)
• pdm run pre-commit run --all-files
• actionlint
• disposable Neon production-data clone: migration preserved all table row counts; runtime readiness passed as inkcre_core
• disposable Neon development clone: duplicate init/seed/reset produced identical baseline fingerprints

Live gate

Production cutover remains gated on this PR's digest-pinned Docker acceptance, a fresh production recovery checkpoint, and exact environment configuration. The unrelated local portless.json is excluded.