@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/geometry/los.py

@@ -0,0 +1,85 @@
+"""
+Line-of-sight checks using terrain profile data.
+"""
+
+import math
+from typing import Optional, Dict, List
+
+EARTH_RADIUS = 6371000
+K_FACTOR = 4 / 3  # Standard atmospheric refraction
+
+
+def check_los_terrain(
+    profile: List[dict],
+    tx_height: float,
+    rx_height: float,
+) -> dict:
+    """
+    Check line-of-sight from a terrain elevation profile.
+
+    Args:
+        profile: List of dicts with 'elevation' and 'distance' keys.
+        tx_height: TX antenna height above ground (meters).
+        rx_height: RX height above ground (meters).
+
+    Returns:
+        dict with has_los, clearance, blocked_at
+    """
+    if not profile:
+        return {"has_los": True, "clearance": 0.0, "blocked_at": None}
+
+    tx_ground = profile[0]["elevation"]
+    rx_ground = profile[-1]["elevation"]
+    tx_total = tx_ground + tx_height
+    rx_total = rx_ground + rx_height
+    total_distance = profile[-1]["distance"]
+
+    min_clearance = float("inf")
+    blocked_at = None
+
+    for point in profile:
+        d = point["distance"]
+        terrain_elev = point["elevation"]
+
+        if total_distance == 0:
+            los_height = tx_total
+        else:
+            los_height = tx_total + (rx_total - tx_total) * (d / total_distance)
+
+        # Earth curvature correction
+        effective_radius = K_FACTOR * EARTH_RADIUS
+        curvature = (d * (total_distance - d)) / (2 * effective_radius)
+        los_height_corrected = los_height - curvature
+
+        clearance = los_height_corrected - terrain_elev
+
+        if clearance < min_clearance:
+            min_clearance = clearance
+            if clearance <= 0:
+                blocked_at = d
+
+    return {
+        "has_los": min_clearance > 0,
+        "clearance": min_clearance,
+        "blocked_at": blocked_at,
+    }
+
+
+def fresnel_radius(
+    d1_m: float, d2_m: float, wavelength_m: float, zone: int = 1
+) -> float:
+    """Calculate Fresnel zone radius at a point along the path.
+
+    Args:
+        d1_m: Distance from TX to point
+        d2_m: Distance from point to RX
+        wavelength_m: Signal wavelength
+        zone: Fresnel zone number (default 1)
+
+    Returns:
+        Radius in meters
+    """
+    total = d1_m + d2_m
+    if total <= 0:
+        return 0.0
+    return math.sqrt(zone * wavelength_m * d1_m * d2_m / total)