@mytec: feat: Phase 3.0 Architecture Refactor ✅

Major refactoring of RFCP backend:
- Modular propagation models (8 models)
- SharedMemoryManager for terrain data
- ProcessPoolExecutor parallel processing
- WebSocket progress streaming
- Building filtering pipeline (351k → 15k)
- 82 unit tests

Performance: Standard preset 38s → 5s (7.6x speedup)

Known issue: Detailed preset timeout (fix in 3.1.0)

backend/app/parallel/__init__.py

@@ -0,0 +1,11 @@
+"""
+Parallel processing infrastructure for coverage calculations.
+"""
+
+from app.parallel.manager import SharedMemoryManager, SharedTerrainData, SharedBuildingData
+from app.parallel.pool import ManagedProcessPool
+
+__all__ = [
+    "SharedMemoryManager", "SharedTerrainData", "SharedBuildingData",
+    "ManagedProcessPool",
+]