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.

src-tauri/src/db.rs

@@ -2624,6 +2624,35 @@ pub fn remove_tag(conn: &Connection, tag_id: i64) -> Result<()> {
     Ok(())
 }
 
+/// Rename a tag across the whole library, or merge it into an existing tag when
+/// `to` already exists. Images that already carry `to` keep a single instance
+/// (the colliding source row is dropped).
+pub fn rename_tag(conn: &Connection, from: &str, to: &str) -> Result<()> {
+    let tx = conn.unchecked_transaction()?;
+    // Move rows where the target tag isn't already on that image; UNIQUE
+    // collisions are skipped (OR IGNORE)…
+    tx.execute(
+        "UPDATE OR IGNORE image_tags SET tag = ?2 WHERE tag = ?1",
+        params![from, to],
+    )?;
+    // …then drop the now-duplicate leftovers still under the old name.
+    tx.execute("DELETE FROM image_tags WHERE tag = ?1", params![from])?;
+    // The tag-cloud cache keys on image-id hashes, not tag text, so a rename
+    // wouldn't invalidate it automatically — clear it.
+    tx.execute("DELETE FROM tag_cloud_cache", [])?;
+    tx.commit()?;
+    Ok(())
+}
+
+/// Delete a tag from every image in the library. Returns the number of rows removed.
+pub fn delete_tag(conn: &Connection, name: &str) -> Result<i64> {
+    let tx = conn.unchecked_transaction()?;
+    let removed = tx.execute("DELETE FROM image_tags WHERE tag = ?1", params![name])? as i64;
+    tx.execute("DELETE FROM tag_cloud_cache", [])?;
+    tx.commit()?;
+    Ok(removed)
+}
+
 pub fn enqueue_missing_tagging_jobs_for_folder(conn: &Connection, folder_id: i64) -> Result<usize> {
     let inserted = conn.execute(
         "INSERT INTO tagging_jobs (image_id, status, attempts, last_error, created_at, updated_at)