Harden live sharing and AI usage controls

[PengfanZ]

What changed

• validate complete Live activity graphs consistently in the browser and database
• let capability holders end a Live session while preserving local recovery copies
• add per-client and project-wide AI text/voice budgets
• trust only the platform-provided client address for AI quota identity
• restrict production CSP connections to the configured Supabase origin
• patch the vulnerable transitive nanoid version
• document the security controls and add a user-facing changelog entry

Why

The previous database snapshot check was shallower than the browser contract, Live capability URLs could not be explicitly revoked, distributed AI traffic had no project-wide ceiling, and release CSP contained development connection sources.

Verification

• 501 Vitest tests with 100% statement, branch, function, and line coverage
• 191 pgTAP database tests after a clean local migration reset
• Supabase schema lint with no errors
• 12 core/PWA/Live Playwright scenarios
• 14 AI text/voice Playwright scenarios
• TypeScript, ESLint, production Pages build, CSP inspection, and diff checks