Squash merge feature/library-reorganization

PLAN.md

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+# Walkup Implementation Plan
+
+## Scope
+- React PWA frontend.
+- FastAPI backend.
+- TeamSnap JavaScript SDK on the client.
+- Server-side TeamSnap OAuth code exchange and refresh.
+- Backend stores only app-owned data and TeamSnap external IDs.
+
+## Initial Deliverables
+- Thin TeamSnap auth/session backend.
+- Media upload and clip registration flow.
+- Game assignment and operator session APIs.
+- Installable React PWA shell with offline-ready game prep scaffolding.
+- Docker-based local development stack.
+
+## Known Constraints
+- TeamSnap entities should not be durably mirrored on the backend.
+- Operator lineup changes are local-session state in v1.
+- Browser clip editing is first-class; backend finalizes playback assets.