feat: frontend MVP — auth, timeline, upload, albums, admin, image viewer

Backend:
- user roles (DB + JWT + first-user-is-admin)
- volume-aware file resolver (multi-volume asset serving)
- directory scanner uses volume URI directly
- date-summary endpoint (capture date from EXIF)
- timeline ordered by capture date
- list endpoints: volumes, plugins, pipelines, library paths
- delete endpoints: volumes, library paths
- configurable upload body limit (MAX_UPLOAD_BYTES)

Frontend:
- auth: login/register, token refresh, role-based admin gate
- timeline: date-grouped grid, infinite scroll, date scrubber
- image viewer: fullscreen zoom/pan/pinch, metadata sidebar
- upload: drag-drop, sequential upload, progress tracking
- albums: create, add/remove photos, asset picker dialog
- admin: storage (import library), jobs (pagination, error details),
  plugins (list + toggle), pipelines, sidecars, duplicates
- multi-select mode with add-to-album action
- TanStack Query for all data fetching

k-photos-frontend/hooks/use-sidecars.ts

@@ -0,0 +1,71 @@
+"use client"
+
+import { useMutation } from "@tanstack/react-query"
+import api from "@/lib/api"
+import type {
+  SidecarExportResponse,
+  SidecarImportResponse,
+  DetectChangesResponse,
+} from "@/lib/types"
+
+export function useExportSidecar() {
+  return useMutation({
+    mutationFn: async (assetId: string) => {
+      const { data } = await api.post<SidecarExportResponse>(
+        `/sidecar/export/${assetId}`,
+      )
+      return data
+    },
+  })
+}
+
+export function useImportSidecar() {
+  return useMutation({
+    mutationFn: async (assetId: string) => {
+      const { data } = await api.post<SidecarImportResponse>(
+        `/sidecar/import/${assetId}`,
+      )
+      return data
+    },
+  })
+}
+
+export function useDetectChanges() {
+  return useMutation({
+    mutationFn: async () => {
+      const { data } =
+        await api.post<DetectChangesResponse>("/sidecar/detect-changes")
+      return data
+    },
+  })
+}
+
+export function useResolveSidecarConflict() {
+  return useMutation({
+    mutationFn: async ({
+      assetId,
+      policy,
+    }: {
+      assetId: string
+      policy: string
+    }) => {
+      await api.post(`/sidecar/resolve/${assetId}`, { policy })
+    },
+  })
+}
+
+export function useFullExport() {
+  return useMutation({
+    mutationFn: async () => {
+      await api.post("/sidecar/full-export")
+    },
+  })
+}
+
+export function useFullImport() {
+  return useMutation({
+    mutationFn: async () => {
+      await api.post("/sidecar/full-import")
+    },
+  })
+}