First commit of claude's rework in django + vanillajs fronted

apps/photos/analysis.py

@@ -0,0 +1,64 @@
+"""
+Group size computation from PointOfImpact real-world coordinates.
+
+All measurements in millimetres. Origin is point-of-aim:
+  x > 0 = right (windage),  y > 0 = up (elevation).
+"""
+import math
+
+
+def compute_group_size(
+    points: list[tuple[float, float]],
+    distance_m: float | None = None,
+) -> dict:
+    """
+    Compute ballistic group metrics from a list of (x_mm, y_mm) coordinates.
+
+    Args:
+        points:     list of (x_mm, y_mm) tuples — minimum 2 required.
+        distance_m: shooting distance in metres, used for MOA conversion.
+                    Pass None to leave MOA fields as None.
+
+    Returns:
+        dict with keys matching GroupPhotoAnalysis fields.
+    """
+    if len(points) < 2:
+        raise ValueError("At least 2 points of impact are required.")
+
+    xs = [p[0] for p in points]
+    ys = [p[1] for p in points]
+    n = len(points)
+
+    # Extreme spread: maximum pairwise distance
+    group_size_mm = 0.0
+    for i in range(n):
+        for j in range(i + 1, n):
+            d = math.sqrt((xs[i] - xs[j]) ** 2 + (ys[i] - ys[j]) ** 2)
+            if d > group_size_mm:
+                group_size_mm = d
+
+    # Centroid
+    cx = sum(xs) / n
+    cy = sum(ys) / n
+
+    # Mean radius: average distance from centroid
+    mean_radius_mm = sum(
+        math.sqrt((x - cx) ** 2 + (y - cy) ** 2) for x, y in points
+    ) / n
+
+    def to_moa(mm: float) -> float | None:
+        """Convert mm at distance_m to MOA. 1 MOA ≈ 0.29089 mm/m at that distance."""
+        if distance_m is None or distance_m <= 0:
+            return None
+        return round(mm / (distance_m * 0.29089), 3)
+
+    return {
+        'group_size_mm':        round(group_size_mm, 2),
+        'group_size_moa':       to_moa(group_size_mm),
+        'mean_radius_mm':       round(mean_radius_mm, 2),
+        'mean_radius_moa':      to_moa(mean_radius_mm),
+        'windage_offset_mm':    round(cx, 2),
+        'windage_offset_moa':   to_moa(cx),
+        'elevation_offset_mm':  round(cy, 2),
+        'elevation_offset_moa': to_moa(cy),
+    }