Fix migration workflow completion

[arjunkomath]

Summary

• replace migration restore success/failure wait race with a single terminal restore-finished event
• keep legacy restore events emitted for in-flight workflow compatibility
• finalize migration state in a separate retry-safe step and let agent status recover legacy target-starting states
• add UI label for the deploying_target migration phase

Verification

• pnpm exec tsc --noEmit --pretty false
• pnpm exec biome check --formatter-enabled=false app/api/v1/agent/restore/complete/route.ts lib/inngest/events/migration.ts lib/inngest/events/index.ts lib/inngest/functions/migration-workflow.ts lib/agent-status.ts components/service/details/deployment-progress.tsx

Review

• reviewed with smart-review; follow-up review reported no blockers

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit ced2cc1.}