feat: multi-instance deployment — all 14 must-have items from spec
CalVer CI (release.yml) with stable/dev channels, health endpoint
with version/channel/schema_version, JWT secret auto-generation with
file persistence, smoke test script + Docker-in-CI, pre-migration
snapshot, /api/admin/configure for headless setup, /api/admin/
discover-and-register, /setup wizard, OpenAPI snapshot test, custom
connector mount support, CHANGELOG, migration safety tests, startup
banner.
663 tests pass (6 new migration safety + 3 OpenAPI snapshot + 1
updated JWT test).
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