Restructure solution layout by module

src/Scheduler/__Libraries/StellaOps.Scheduler.ImpactIndex/REMOVAL_NOTE.md

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+# ImpactIndex Stub Removal Tracker
+
+- **Created:** 2025-10-20
+- **Owner:** Scheduler ImpactIndex Guild
+- **Reference Task:** SCHED-IMPACT-16-300 (fixture-backed stub)
+
+## Exit Reminder
+
+Replace `FixtureImpactIndex` with the roaring bitmap-backed implementation once SCHED-IMPACT-16-301/302 are completed, then delete:
+
+1. Stub classes (`FixtureImpactIndex`, `ImpactIndexStubOptions`, `ImpactIndexServiceCollectionExtensions`).
+2. Embedded sample fixture wiring in `StellaOps.Scheduler.ImpactIndex.csproj`.
+3. Temporary unit tests in `StellaOps.Scheduler.ImpactIndex.Tests`.
+
+Remove this file when the production ImpactIndex replaces the stub.