feat: lightbox EXIF panel, tag management, reorderable albums

EXIF info panel:
- New on-demand get_image_exif command (kamadak-exif) returning camera/lens/
  aperture/shutter/ISO/focal-length and decimal GPS; read from the file when the
  lightbox opens (no DB schema change, works on already-indexed images).
- Lightbox shows a Camera panel; GPS opens the location in the browser via
  OpenStreetMap (adds opener:allow-open-url capability).

Tag management:
- Backend rename_tag (rename, or merge when the target exists) and delete_tag
  (library-wide), both clearing the tag-cloud cache; store actions invalidate
  tag caches, refresh Explore, and re-point/refresh an active tag-search.
- Explore -> Tag Cloud gains a Manage mode: a flat list with per-tag rename/
  merge/delete.

Albums:
- Drag-to-reorder in the sidebar via framer-motion Reorder with a hover handle;
  order persists through the existing reorder_albums command.

Reads live store order on drag end and robustly derives GPS hemisphere from raw
EXIF ref bytes (review follow-ups). CHANGELOG updated.

CHANGELOG.md

@@ -24,6 +24,17 @@ aims to follow [Semantic Versioning](https://semver.org/spec/v2.0.0.html)
   views too.
 - **Build badge in Settings** — the version line in Settings → Updates now shows
   whether the running build is the CPU or CUDA (GPU-accelerated) variant.
+- **Camera info in the lightbox** — the image info panel now shows EXIF details
+  (camera, lens, aperture, shutter, ISO, focal length) and, when a photo is
+  geotagged, its GPS coordinates as a link that opens the location in your
+  browser. Read on demand from the file, so it works on already-indexed images
+  without re-indexing.
+- **Tag management** — Explore → Tag Cloud gains a Manage mode with a flat tag
+  list where you can rename a tag, merge it into another (rename it to an
+  existing tag's name), or delete it from every image. Changes apply across the
+  whole library.
+- **Reorderable albums** — drag albums in the sidebar (hover the row for the
+  drag handle) to set their order, which persists across sessions.
 - **What's New** — after updating, Phokus now greets you with a "What's new"
   toast that opens an in-app release-notes screen for the new version, with the
   changes grouped into collapsible Added / Changed / Fixed sections. It's