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/preview/PreviewView.tsx

@@ -1,8 +1,10 @@
 import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
+import { useQuery } from '@tanstack/react-query'
 import { useHotkeys } from 'react-hotkeys-hook'
 import { X, Info } from 'lucide-react'
 import { usePhotoStore } from '../../store/photoStore'
 import { usePhotosQuery } from '../../hooks/usePhotosQuery'
+import { photos as photosApi } from '../../services/api'
 import type { Photo } from '../../types/photo'
 import { PreviewImage } from './PreviewImage'
 import { PreviewFilmstrip } from './PreviewFilmstrip'
@@ -43,7 +45,24 @@ export function PreviewView() {
     ? photos.findIndex((p) => p.id === activePhotoId)
     : 0
   const safeIndex = currentIndex < 0 ? 0 : currentIndex
-  const currentPhoto: Photo | undefined = photos[safeIndex]
+
+  // Fallback fetch: when the preview is opened for a photo that isn't in
+  // the timeline query result (e.g. clicked from the Map view, where the
+  // active section's filter excludes it), look it up by id directly.
+  // PhotoInfoPanel runs the same query under the same key, so they share
+  // one cache entry — no extra request.
+  const photoInListById = activePhotoId
+    ? photos.find((p) => p.id === activePhotoId)
+    : undefined
+  const { data: standalonePhoto } = useQuery<Photo>({
+    queryKey: ['photo', activePhotoId],
+    queryFn: () => photosApi.get(activePhotoId as string),
+    enabled: !!activePhotoId && !photoInListById,
+    staleTime: 60_000,
+  })
+
+  const currentPhoto: Photo | undefined =
+    photoInListById ?? photos[safeIndex] ?? standalonePhoto
 
   // Keep the latest photos array + active id in a ref so the keyboard
   // handlers ALWAYS read the freshest state. Without this, react-hotkeys-