refactor: route market providers through data gateway

docs/governance/architecture-inventory.json

@@ -265,8 +265,8 @@
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docs/governance/stage-06-data-gateway.md

@@ -0,0 +1,29 @@
+# Stage 06: Unified Data Gateway
+
+Date: 2026-07-29
+
+## Result
+
+- Added canonical provider and dataset contracts under `backend/data`.
+- Added `DataSourcePolicy`, loaded from the Stage 04 data registry.
+- Added provider adapters for Tushare and iFinD.
+- Added one `DataGateway` that owns Tushare creation, the shared iFinD client, chart routing,
+  and isolated Eastmoney/Tencent realtime observation.
+- Replaced all real `DashboardService` Tushare construction paths with the gateway.
+- Kept one compatibility constructor for unit tests that instantiate an incomplete service with
+  `__new__`; production instances never use it.
+- The Tushare token is supplied lazily, so administrator credential changes do not leave a
+  stale client in memory.
+
+## Enforcement Introduced
+
+- Unregistered datasets fail.
+- Blocked datasets fail.
+- Public-web providers cannot be promoted to calculation inputs through a fallback call.
+- Display chart fallbacks remain distinct from deterministic calculation datasets.
+
+## Deferred to Stage 07
+
+Stage 06 centralizes provider access but does not yet attach freshness, coverage, unit, and
+point-in-time quality evidence to every returned observation. Stage 07 introduces those gates
+without changing provider routing again.