Replace #[allow(dead_code)] on server-only helpers with #[cfg(feature = "server")]
to make the server/WASM split explicit and avoid compiling unused server logic
into the WASM frontend.
- Gate password/session/auth/comment helpers and model parsers with server feature
- Gate related imports and tests accordingly
- Remove genuinely unused CreatePostRequest and CreateCommentRequest
- Keep #[allow(dead_code)] for true dead code (stub methods, unused public APIs)
- Use #[cfg(any(target_arch = "wasm32", test))] for THEME_KEY
- Update AGENTS.md note
- Cache ammonia::Builder with LazyLock (was rebuilt per request)
- Enable tracing release_max_level_info to strip tracing overhead at compile time
- Remove TraceLayer and tower-http trace feature from production
- Increase DB pool size 10→20 (configurable via DB_POOL_SIZE)
- Increase SSR cache TTL 300s→3600s (configurable via SSR_CACHE_SECS)
Benchmark: 7,444 → 9,840 req/s, P99 latency 27.6ms → 11.1ms
