@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/propagation/longley_rice.py

@@ -0,0 +1,75 @@
+"""
+Longley-Rice Irregular Terrain Model (ITM).
+
+Best for:
+- VHF/UHF over irregular terrain
+- Point-to-point links
+- Distances 1-2000 km
+
+Note: This is a simplified area-mode version.
+Full implementation requires terrain profile data.
+
+Reference: NTIA Report 82-100
+"""
+
+import math
+from app.propagation.base import PropagationModel, PropagationInput, PropagationOutput
+
+
+class LongleyRiceModel(PropagationModel):
+
+    @property
+    def name(self) -> str:
+        return "Longley-Rice"
+
+    @property
+    def frequency_range(self) -> tuple:
+        return (20, 20000)  # 20 MHz to 20 GHz
+
+    @property
+    def distance_range(self) -> tuple:
+        return (1000, 2000000)  # 1-2000 km
+
+    def calculate(self, input: PropagationInput) -> PropagationOutput:
+        """
+        Simplified Longley-Rice (area mode).
+
+        For proper implementation, use splat! or NTIA ITM reference.
+        """
+        f = input.frequency_mhz
+        d = max(input.distance_m / 1000, 1.0)
+        h1 = max(input.tx_height_m, 1.0)
+        h2 = max(input.rx_height_m, 1.0)
+
+        # Terrain irregularity parameter (simplified)
+        delta_h = input.terrain_roughness_m or 90  # Default: rolling hills
+
+        # Free space loss
+        L_fs = 32.45 + 20 * math.log10(d) + 20 * math.log10(f)
+
+        # Terrain clutter loss (simplified)
+        if delta_h < 10:
+            L_terrain = 0  # Flat
+        elif delta_h < 50:
+            L_terrain = 5  # Gently rolling
+        elif delta_h < 150:
+            L_terrain = 10  # Rolling hills
+        else:
+            L_terrain = 15  # Mountains
+
+        # Height gain
+        h_eff = h1 + h2
+        height_gain = 10 * math.log10(h_eff / 20) if h_eff > 20 else 0
+
+        L = L_fs + L_terrain - height_gain
+
+        return PropagationOutput(
+            path_loss_db=L,
+            model_name=self.name,
+            is_los=delta_h < 10 and d < 10,
+            breakdown={
+                "free_space_loss": L_fs,
+                "terrain_loss": L_terrain,
+                "height_gain": height_gain,
+            },
+        )