refactor: establish feature application service layout

docs/governance/stage-10-feature-services.md

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+# Stage 10: Feature Application Service Layout
+
+Date: 2026-07-29
+
+## Result
+
+- Created the governed `backend/features/<feature>` source boundary.
+- Moved alert behavior into the alerts feature.
+- Moved trade-journal behavior into the review feature.
+- Moved strategy-tracking behavior into the screener feature.
+- Changed the application container to import feature-owned services directly.
+- Reduced the former top-level service modules to compatibility exports, preserving existing
+  imports without maintaining duplicate implementations.
+- Added dependency tests that prevent feature services from importing HTTP delivery code or
+  concrete market-provider adapters.
+
+## Template
+
+Each migrated feature owns its application behavior and depends on repository or gateway
+ports. HTTP delivery and background jobs may invoke the service, but neither may become the
+owner of its rules. The same layout is now available for the remaining market, account,
+Mentor, Wentian, and screener services.
+
+## Compatibility
+
+No route, response shape, persisted data, service method, or top-level import path changes in
+this stage. Compatibility exports are removed only after all internal and external callers
+use the feature packages.