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/agents/repo-scout.toml

@@ -0,0 +1,11 @@
+name = "repo_scout"
+description = "Read-only Sauci codebase scout for locating ownership, callers, contracts, tests, and existing patterns."
+model = "gpt-5.6-luna"
+model_reasoning_effort = "low"
+sandbox_mode = "read-only"
+developer_instructions = """
+Read the root and nearest scoped AGENTS.md files. Map only the requested surface.
+Return evidence-backed file paths, symbols, current behavior, dependencies, tests,
+and uncertainties. Do not edit files, make design decisions, or propose broad
+refactors. Do not claim runtime behavior you did not observe.
+"""