[spelech]

Fixes #50.

Changes

• Import SQLAlchemy text for the native PostgreSQL readiness path.
• Add real PostgreSQL, isolated-schema regressions covering all readiness aliases, missing-table HTTP 503 sanitization and independent liveness.

Verification

• Before the fix: initialized native PostgreSQL returned HTTP 503 because text was undefined.
• Native PostgreSQL and existing SQLite readiness selection: 6 passed.
• Generated requirement inventory: 2 passed; release/link-integrity gate passed.
• Combined backend-fix regression run: 70 passed, 1 skipped.

Native tests require TEST_POSTGRES_URL and create/remove only uniquely named test schemas. These are focused cached-runtime checks, not a claim that the full suite or a fresh source build passes.