fix(ttl): reconcile closed pull request namespaces

[vigneshrajsb]

Summary

• Teach TTL cleanup to treat expired namespaces for non-open pull requests as cleanup targets instead of skipping them.
• Reuse the existing BuildService.deleteQueue for closed/merged PR teardown so the TTL worker remains a scanner/reconciler and teardown stays in the existing delete path.
• Preserve the current open-PR TTL behavior that updates labels and posts the inactivity comment.
• Add focused TTL service tests using neutral dummy repositories and namespace data.

Root cause

TTL cleanup previously only handled expired namespaces tied to open pull requests. If a close webhook or an in-flight deploy race left a closed-PR namespace behind, TTL would load the build and PR, see pullRequest.status !== 'open', and skip it forever.

Validation

• pnpm test -- src/server/services/__tests__/ttlCleanup.test.ts passed.
• pnpm test passed: 178 suites, 1605 tests.
• pnpm run lint passed.
• pnpm exec prettier --check src/server/services/ttlCleanup.ts src/server/services/__tests__/ttlCleanup.test.ts passed.
• git diff --check passed.
• pnpm run ts-check still fails on existing repo-wide type errors outside this change, including stale .next/types route references, script strict-null errors, and unrelated service/model strictness issues. After fixing the optional comment fields in ttlCleanup.ts, the rerun no longer reports ttlCleanup.ts errors.