AD-802: Add patch proposal service

[alph-cmky]

Summary

• Add PatchProposal schema with target metadata, base version, JSON patch operations, validation result, approval state, and diff preview.
• Add an in-memory patch proposal service for workflow patch preview without mutating the target workflow.
• Validate patched workflow previews through workflow-core and require approval before apply.
• Stabilize the daemon SSE disconnect test by waiting for the close cleanup instead of relying on a fixed 10ms delay.
• Update the AD-802 backlog checklist.

Testing

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

Stacked on #45.

Closes #21