feat: editable taken_at + folder-based date repair and filter

Lets operators fix corrupted capture dates at scale. Adds an editable
Date Taken field with a folder/filename-derived suggestion hint, a bulk
Date Taken section in the multi-select sidebar that either applies one
date to the whole selection or infers a per-photo date from each path,
a warning badge on thumbnails whose stored date disagrees with the
path, and a "Date issues" filter pill so suspicious photos can be
surfaced and fixed as a group. Edits are written back to EXIF on disk
so rescans don't clobber the fix.

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

frontend/src/services/api.ts

@@ -185,6 +185,39 @@ export const photos = {
     return response.data
   },
 
+  /** Bulk set taken_at — one ISO datetime applied to every listed photo.
+   *  Backend rewrites EXIF on disk per-photo and surfaces per-photo errors
+   *  in the `errors` array so the UI can report a partial apply. */
+  bulkSetTakenAt: async (photoIds: string[], isoDatetime: string) => {
+    const response = await api.post('/photos/bulk', {
+      ids: photoIds,
+      action: 'set_taken_at',
+      value: isoDatetime,
+    })
+    return response.data as {
+      status: string
+      updated: number
+      skipped: number
+      errors: { id: string; message: string }[]
+    }
+  },
+
+  /** Bulk set taken_at with a per-photo map. Used by the "guess from folder"
+   *  flow where every selected photo gets its own suggested date. */
+  bulkSetTakenAtMap: async (map: Record<string, string>) => {
+    const response = await api.post('/photos/bulk', {
+      ids: Object.keys(map),
+      action: 'set_taken_at_map',
+      value: map,
+    })
+    return response.data as {
+      status: string
+      updated: number
+      skipped: number
+      errors: { id: string; message: string }[]
+    }
+  },
+
   /** Add the listed tags to every listed photo. Idempotent — re-adding
    *  an existing (photo, tag) pair is a no-op. Returns { added: N }. */
   bulkAddTags: async (photoIds: string[], tagIds: string[]) => {