Database intelligence and access WIP checkpoint

[BigSimmo]

Summary

• Checkpoints the current Database WIP around document intelligence/index units, API rate limiting, protected access routes, and dashboard shell extraction.
• Rebases that WIP onto current origin/main so it is no longer loose local work on the old safe-save branch.
• Keeps this PR draft because the change set is broad and should be reviewed/sliced before merge.

Verification

• npm run typecheck
• npx vitest run tests/deep-memory.test.ts tests/private-access-routes.test.ts tests/private-rag-access.test.ts tests/source-governance.test.ts tests/supabase-schema.test.ts tests/document-index-units.test.ts tests/model-index-extraction.test.ts
• npm run lint