Establish governance docs as canonical repo context

docs/00-governance/architecture.md

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+# Architecture Governance
+
+## Runtime Flow (Authoritative)
+```
+SimpleORBNT8.cs
+  -> NT8StrategyBase.cs
+  -> SimpleORBStrategy.cs
+  -> NT8OrderAdapter.cs
+  -> PortfolioRiskManager.cs
+  -> NinjaTrader 8
+```
+
+## Responsibilities
+- `SimpleORBNT8.cs`: NT8 entry point and platform lifecycle bridge.
+- `NT8StrategyBase.cs`: orchestration, risk gate sequencing, execution handoff, platform callbacks.
+- `SimpleORBStrategy.cs`: signal generation and confluence grading only.
+- `NT8OrderAdapter.cs`: execution bridge to NT8 managed order APIs.
+- `PortfolioRiskManager.cs`: cross-strategy risk controls and account-level enforcement.
+
+## Architectural Constraints
+- Risk-first flow is mandatory; no strategy-level bypass of risk validation.
+- Managed-order sequence remains required (`SetStopLoss` / `SetProfitTarget` before entry).
+- C# 5.0 syntax only, .NET Framework 4.8 only.
+- NT8 signatures must be verified against official NinjaTrader docs before API-touching edits.
+
+## Governance Notes
+- Core Risk/Sizing/OMS/Intelligence/Analytics layers are treated as complete and stable unless explicitly re-opened by approved work.
+- Hardening changes are concentrated in targeted adapter/utility components per active-work scope.