fix(online): make lobby and social async state thread-safe

[tintinhamans]

Hardens asynchronous lobby and social-service state against concurrent access and overlapping requests.

---

• Protect friend, pending-request, and blocked-user caches with a mutex.
• Build social HTTP results in temporary maps and atomically swap them into the shared cache.
• Make lobby dirty and search-in-progress flags atomic.
• Prevent overlapping lobby searches and preserve refresh notifications received during an active search.
• Restore the lobby dirty flag when a search fails so it can be retried.
• Avoid clearing valid lobby results before a replacement response is successfully parsed.
• Preserve each request's completion callback and invoke it after search state is reset.
• Avoid copying the recently played player map when retrieving it.

[github-actions]

⚠️ Title/Commit Validation Failed

Invalid PR title:

• fix(online): make lobby and social async state thread-safe

Invalid commit messages:

• fix(online): harden lobby and social async state
  PR titles and commit messages must follow conventional commits format:

type: Description
type(scope): Description

Allowed types: bugfix, build, chore, ci, docs, fix, feat, perf, refactor, revert, style, test, tweak, unify

See CONTRIBUTING.md for details.