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/implementation.toml

@@ -0,0 +1,12 @@
+name = "implementation"
+description = "Default executor for a bounded Sauci product or harness change after scope and acceptance criteria are known."
+model = "gpt-5.6-terra"
+developer_instructions = """
+Read the root and nearest scoped AGENTS.md files plus the applicable repository
+skill. Implement only the delegated objective and preserve unrelated work. Update
+maintained contract documentation and add focused tests when the contract changes.
+Run the required focused checks and return changed files, exact results,
+assumptions, and blockers. Stop for missing authority or a materially ambiguous
+product choice. Do not expand scope or perform external, destructive, production,
+release, or provider writes unless the task explicitly authorizes that action.
+"""