Interpolate sparse horizon CSVs instead of rejecting them

Any CSV with ≥ 2 az_deg,alt_deg rows now works. Points are sorted by
azimuth, then linearly interpolated to fill all 360 degrees. A 28-point
sparse horizon profile interpolates cleanly; an exact 360-point file is
used as-is. Also resets the file input after upload so re-uploading the
same file works without picking a different one first.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/Settings.tsx

@@ -359,20 +359,44 @@ export default function Settings() {
   const handleHorizonCSV = async (e: React.ChangeEvent<HTMLInputElement>) => {
     const file = e.target.files?.[0];
     if (!file) return;
+    // Reset input so the same file can be re-uploaded after a reset
+    e.target.value = '';
     const text = await file.text();
-    const lines = text.trim().split('\n').slice(1); // skip header
-    const points: HorizonPoint[] = [];
-    for (const line of lines) {
+    const raw: HorizonPoint[] = [];
+    for (const line of text.trim().split('\n')) {
       const [az, alt] = line.split(',').map(Number);
       if (!isNaN(az) && !isNaN(alt)) {
-        points.push({ az_deg: Math.round(az) % 360, alt_deg: Math.max(0, Math.min(90, alt)) });
+        raw.push({ az_deg: ((Math.round(az) % 360) + 360) % 360, alt_deg: Math.max(0, Math.min(90, alt)) });
       }
     }
-    if (points.length === 360) {
-      setHorizon.mutate(points);
-    } else {
-      alert(`CSV must have exactly 360 rows (got ${points.length}). Format: az_deg,alt_deg`);
+    if (raw.length < 2) {
+      alert('CSV must have at least 2 valid az_deg,alt_deg rows.');
+      return;
     }
+    // Sort by azimuth
+    raw.sort((a, b) => a.az_deg - b.az_deg);
+
+    // If already 360 points, use as-is; otherwise interpolate to fill every degree
+    let full: HorizonPoint[];
+    if (raw.length === 360) {
+      full = raw;
+    } else {
+      // Wrap around: append first point at az+360 to close the circle
+      const pts = [...raw, { az_deg: raw[0].az_deg + 360, alt_deg: raw[0].alt_deg }];
+      full = Array.from({ length: 360 }, (_, deg) => {
+        // Find the two surrounding control points
+        let lo = pts[0], hi = pts[pts.length - 1];
+        for (let i = 0; i < pts.length - 1; i++) {
+          if (pts[i].az_deg <= deg && pts[i + 1].az_deg >= deg) {
+            lo = pts[i]; hi = pts[i + 1]; break;
+          }
+        }
+        const span = hi.az_deg - lo.az_deg;
+        const t = span > 0 ? (deg - lo.az_deg) / span : 0;
+        return { az_deg: deg, alt_deg: Math.max(0, lo.alt_deg + t * (hi.alt_deg - lo.alt_deg)) };
+      });
+    }
+    setHorizon.mutate(full);
   };
 
   const resetHorizon = () => {
@@ -396,7 +420,7 @@ export default function Settings() {
           {horizonData?.points && <HorizonPolarChart points={horizonData.points} />}
           <div style={{ display: 'flex', flexDirection: 'column', gap: 10 }}>
             <div style={{ fontSize: 12, color: 'var(--text-mid)', maxWidth: 300 }}>
-              Upload a CSV file with columns <code>az_deg,alt_deg</code>, one row per degree (360 rows total).
+              Upload a CSV with columns <code>az_deg,alt_deg</code>. Sparse files (any number of points ≥ 2) are linearly interpolated to 360°.
             </div>
             <label style={{
               display: 'inline-flex',