perf(app): reduce redundant data fetching

Share bounded database pools across API repositories, consolidate sync and chat queries, and make mobile refreshes cache-aware and foreground-aware.

Add focused regression coverage, client freshness documentation, and repository agent role configuration.

.codex/config.toml

@@ -0,0 +1,5 @@
+[agents]
+enabled = true
+max_concurrent_threads_per_session = 3
+default_subagent_model = "gpt-5.6-terra"
+default_subagent_reasoning_effort = "medium"