Fix multi-sensor cameras collapsing into one tile

Channels were keyed solely on the metadata `Name` field. Multi-sensor
cameras (e.g. Avigilon 32C-H5A) export one file per sensor that share an
identical `Name` and `Serial`, so their sensors merged into a single tile
and one sensor's clips were lost to start-time dedup — surfacing as
"only 3 of 4 cameras loaded".

Add cameraIdFromFile(), which derives a per-sensor id from the export
filename prefix (stripping the Alta timestamp, e.g. "Backyard_4-...Z.mp4"
-> "Backyard 4"), and key channels by it, falling back to the metadata
Name for non-Alta filenames. Verified: all 4 sensors now load as
distinct tiles (4 cameras | 13 clips).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

templates/index.html

@@ -1623,6 +1623,20 @@
     return name.replace(/\.(mp4|mov|avi|mkv|txt)$/i, '');
   }
 
+  // Derive a per-sensor camera id from an Alta export filename by stripping the
+  // trailing timestamp, e.g. "Backyard_4-2026-06-03T10-02-48.000Z.mp4" -> "Backyard 4".
+  // Multi-sensor cameras (e.g. Avigilon 32C-H5A) export one file per sensor that
+  // share the SAME metadata Name and Serial, so the filename prefix is the only
+  // thing distinguishing the sensors. Keying channels by it stops distinct sensors
+  // from collapsing into one tile. Returns '' when no Alta timestamp is present so
+  // callers can fall back to the metadata Name.
+  function cameraIdFromFile(fileName) {
+    const base = baseName(fileName);
+    const stripped = base.replace(/-\d{4}-\d{2}-\d{2}T[\d\-.]+Z?$/i, '');
+    if (stripped === base) return '';
+    return stripped.replace(/_/g, ' ').trim();
+  }
+
   // ─── Channel / Segment Management ───
 
   function getOrCreateChannel(name) {
@@ -1700,7 +1714,7 @@
       for (let mi = pendingMetas.length - 1; mi >= 0; mi--) {
         const m = pendingMetas[mi];
         if (vBase === baseName(m.fileName)) {
-          const cameraName = m.meta['Name'] || `Camera ${channels.size + 1}`;
+          const cameraName = cameraIdFromFile(v.fileName) || m.meta['Name'] || `Camera ${channels.size + 1}`;
           addSegment(cameraName, m.meta, v.blob);
           pendingVideos.splice(vi, 1);
           pendingMetas.splice(mi, 1);
@@ -1717,7 +1731,7 @@
 
     // Remaining videos without metadata
     for (const v of pendingVideos) {
-      const name = baseName(v.fileName).replace(/_/g, ' ');
+      const name = cameraIdFromFile(v.fileName) || baseName(v.fileName).replace(/_/g, ' ');
       const ch = getOrCreateChannel(name);
       const url = URL.createObjectURL(v.blob);
       ch.segments.push({ startTime: null, endTime: null, url, blob: v.blob, meta: {}, videoEl: null, loaded: false });