docs(database): plugin guide + CLAUDE.md polish + small public-API tweaks

[ditadi]

🥞 Stacked PR

Use this link to review incremental changes.

• stack/database/foundation [Files changed]
  • stack/database/server [Files changed]
    • stack/database/brownfield [Files changed]
      • stack/database/init [Files changed]
        • stack/database/frontend [Files changed]
          • stack/database/ui [Files changed]
            • stack/database/advanced [Files changed]
              • stack/database/release [Files changed]

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Summary

Final polish on top of the stack:

• Plugin guide: docs/docs/plugins/database.md (end-to-end usage, RLS, drift, pool sizing math, known beta limitations)
• Concise Database Plugin section in CLAUDE.md
• defineSchema options parameter optional (typedoc clarity)
• EntityClientImpl explicit implements EntityClient clause
• getDrizzle() reference replaced with getPool() in docs and code

Stack (8/8)

1. #354 foundation
2. #355 server
3. #356 brownfield
4. #357 init
5. #358 frontend
6. #359 ui
7. #360 advanced
8. release ← this PR

Test plan

• biome check
• typecheck
• vitest (full suite — 2052 tests passing)