fix: four review issues (search cap, tagging pause, stale tag, walkdir)

- commands: semantic search doubling loop now returns when batch reaches
  the 8192 cap rather than re-fetching the same IDs forever when filters
  yield fewer than limit matches (P1 infinite loop)

- db/indexer: tagging worker checks is_tagging_job_processing instead
  of is_tagging_job_cancelled so paused jobs reset to 'pending' are also
  discarded; cancelled rows are deleted, paused rows kept for retry

- Lightbox: capture image id at form-submit time and compare against
  currentImageIdRef in the addUserTag callback, matching the guard
  already applied to the getImageTags effect

- indexer: WalkDir errors are no longer silently swallowed; paths under
  unreadable subtrees are excluded from the missing-file deletion pass
  using Path::starts_with (component-aware) so a transient permission
  error cannot cascade into data loss or affect sibling directories

src-tauri/src/commands.rs

@@ -571,6 +571,11 @@ pub async fn semantic_search_images(
             images.truncate(limit);
             return Ok(images);
         }
+        // If we are already at the fetch cap, another iteration would fetch the
+        // exact same IDs — break out rather than looping forever.
+        if batch >= 8192 {
+            return Ok(images);
+        }
         batch = (batch * 2).min(8192);
     }
 }