AD-902: Add audit log service

[alph-cmky]

Summary

• Add audit schema for task execution, patch proposal, approval decision, and sensitive action records.
• Add an in-memory audit log service that records actor, task, agent, runtime, patch proposal, command summary, diff summary, approval decision, metadata, and timestamps.
• Add task/runtime/actor query helpers so audits can answer who changed what, when, through which agent/runtime, and with which approval.
• Redact secret-like values in command summaries, diff summaries, and nested metadata before persistence.
• Export audit APIs from the server package and update the AD-902 backlog checklist.

Testing

• TDD red check: pnpm test apps/server/src/audit/audit-service.test.ts initially failed because audit-service.js did not exist.
• pnpm test apps/server/src/audit/audit-service.test.ts
• pnpm lint && pnpm format && pnpm typecheck && pnpm test && pnpm build

Stacked on #47.

Closes #23