feat: map view with GPS extraction fix

Adds a new Map sidebar entry that plots photos by their EXIF GPS
coordinates on a clustered Leaflet map. While wiring this up, the
metadata extractor was reading unprefixed GPS keys that never exist
in `exiftool -G -j` output AND assumed coordinates were already
floats — every photo silently lost its GPS. The new extract_gps
helper handles Composite/EXIF group prefixes and parses DMS strings,
and lat/lon are stored as first-class indexed columns so the map
can query them without parsing exif_json on every request.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/sidebar/PhotoInfoPanel.tsx

@@ -49,9 +49,20 @@ interface PhotoDetails {
   user_notes: string | null
   color_label: string | null
   exif_json: string | null
+  latitude?: number | null
+  longitude?: number | null
   tags?: PhotoTagSummary[]
 }
 
+/** Format a signed decimal degree value with the hemisphere letter, e.g.
+ *  ``48.12777° N``. Keeps the panel readable without dragging in a heavy
+ *  formatting lib. */
+function formatLatLon(value: number, axis: 'lat' | 'lon'): string {
+  const abs = Math.abs(value).toFixed(5)
+  const ref = axis === 'lat' ? (value >= 0 ? 'N' : 'S') : (value >= 0 ? 'E' : 'W')
+  return `${abs}° ${ref}`
+}
+
 interface ExifData {
   Make?: string
   Model?: string
@@ -547,13 +558,20 @@ export function PhotoInfoPanel({ photoId, darkTheme = false }: PhotoInfoPanelPro
           expanded={expandedSections.has('location')}
           onToggle={() => toggleSection('location')}
         >
-          {exif.GPSLatitude && exif.GPSLongitude ? (
-            <div className="flex items-center gap-2 text-xs">
+          {photo.latitude != null && photo.longitude != null ? (
+            <a
+              href={`https://www.openstreetmap.org/?mlat=${photo.latitude}&mlon=${photo.longitude}#map=15/${photo.latitude}/${photo.longitude}`}
+              target="_blank"
+              rel="noreferrer"
+              className="flex items-center gap-2 text-xs hover:underline"
+              title="Open in OpenStreetMap"
+            >
               <MapPin className="h-3 w-3 text-text-muted" />
               <span className="font-mono text-text">
-                {String(exif.GPSLatitude)}, {String(exif.GPSLongitude)}
+                {formatLatLon(photo.latitude, 'lat')},{' '}
+                {formatLatLon(photo.longitude, 'lon')}
               </span>
-            </div>
+            </a>
           ) : (
             <div className="text-xs text-text-muted">No GPS data</div>
           )}