Serve Flipper Cloud reads from memory

[jnunemaker]

Summary

• Serve Flipper Cloud feature reads from one process-local, thread-safe Memory adapter.
• Hydrate Memory once from the configured local adapter, then mirror explicit writes to persistence and Memory on the calling thread.
• Keep background polling limited to the HTTP fetch; apply synchronization diffs and local adapter mutations on the calling thread.
• Preserve standard config.use wrapper composition and leave cloudless Flipper behavior unchanged.

Compatibility note

• Wrappers configured through config.use continue to govern reads and writes.
• Wrappers manually embedded inside local_adapter govern the persistent side; reads are served by Memory.

Test Coverage

All new code paths have test coverage, including concurrent one-time hydration, memory-only reads, caller-thread writes, poll diff application, and adapter wrapper ordering.

Pre-Landing Review

No issues found.

Design Review

No frontend files changed — design review skipped.

Eval Results

No prompt-related files changed — evals skipped.

Plan Completion

No plan file detected.

Documentation

• README.md: clarified that Flipper Cloud serves reads from process-local memory while keeping the configured local adapter synchronized.

Test plan

• Focused Cloud and adapter suite: 116 examples, 0 failures
• git diff --check
• Previous branch head passed the full GitHub Actions CI and Examples workflows; the updated head will run the same checks after this PR is opened