docs(deploy): add production runbook

[Vann-Dev]

Summary

• Add a production deployment runbook covering required env vars, managed/external Postgres guidance, backups, migration deploy, startup, health/readiness, smoke checks, logs, and rollback caveats.
• Update README deployment section to point operators to the runbook and clarify one-off migrations plus multi-replica startup migration limitations.

Checks

• corepack pnpm lint
• DATABASE_URL=postgresql://user:pass@localhost:5432/db?schema=public corepack pnpm typecheck
• DATABASE_URL=postgresql://user:pass@localhost:5432/db?schema=public AUTH_SECRET=placeholder-for-build-check corepack pnpm build

Build warnings: existing Next.js middleware deprecation warning and jose Edge Runtime CompressionStream/DecompressionStream warnings.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
agent-bridge	Error		May 12, 2026 9:19pm