@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/core/grid.py

@@ -0,0 +1,83 @@
+"""
+Grid generation for coverage calculations.
+"""
+
+import numpy as np
+from dataclasses import dataclass
+from typing import List, Tuple
+from app.geometry.haversine import haversine_distance
+
+
+@dataclass
+class BoundingBox:
+    min_lat: float
+    min_lon: float
+    max_lat: float
+    max_lon: float
+
+
+@dataclass
+class Grid:
+    points: List[Tuple[float, float]]
+    bounding_box: BoundingBox
+    resolution: float
+    radius: float
+
+
+class GridService:
+    """Generate coverage grid points."""
+
+    @staticmethod
+    def generate(
+        center_lat: float,
+        center_lon: float,
+        radius: float,
+        resolution: float,
+    ) -> Grid:
+        points = []
+
+        lat_step = resolution / 111000
+        lon_step = resolution / (111000 * np.cos(np.radians(center_lat)))
+
+        lat_delta = radius / 111000
+        lon_delta = radius / (111000 * np.cos(np.radians(center_lat)))
+
+        bbox = BoundingBox(
+            min_lat=center_lat - lat_delta,
+            min_lon=center_lon - lon_delta,
+            max_lat=center_lat + lat_delta,
+            max_lon=center_lon + lon_delta,
+        )
+
+        lat = center_lat - lat_delta
+        while lat <= center_lat + lat_delta:
+            lon = center_lon - lon_delta
+            while lon <= center_lon + lon_delta:
+                dist = haversine_distance(center_lat, center_lon, lat, lon)
+                if dist <= radius:
+                    points.append((lat, lon))
+                lon += lon_step
+            lat += lat_step
+
+        return Grid(points=points, bounding_box=bbox, resolution=resolution, radius=radius)
+
+    @staticmethod
+    def generate_multi_site(sites: list, radius: float, resolution: float) -> Grid:
+        all_points = set()
+        min_lat = min_lon = float("inf")
+        max_lat = max_lon = float("-inf")
+
+        for site in sites:
+            grid = GridService.generate(site.lat, site.lon, radius, resolution)
+            for p in grid.points:
+                all_points.add((round(p[0], 7), round(p[1], 7)))
+            min_lat = min(min_lat, grid.bounding_box.min_lat)
+            min_lon = min(min_lon, grid.bounding_box.min_lon)
+            max_lat = max(max_lat, grid.bounding_box.max_lat)
+            max_lon = max(max_lon, grid.bounding_box.max_lon)
+
+        return Grid(
+            points=list(all_points),
+            bounding_box=BoundingBox(min_lat, min_lon, max_lat, max_lon),
+            resolution=resolution, radius=radius,
+        )