fix(review): harden write-back, confirmation gate, and edge cases

- write-back: call upsert_tag inside _apply_tag's try so a tag-create failure
  is caught per-asset and apply_all no longer aborts mid-batch (was P1)
- write-back: surface _pipeline/processed write failures in the result instead
  of discarding them (was reported as success)
- ui: add title to the high confidence badge so approve-high-confidence's
  pre-action count is non-zero; confirm() before single-cluster apply
- core: Store context manager; close DB connection even if a route raises;
  guard split_cluster against a first-member boundary (empty cluster); add
  writeback_log lookup index
- ingest: split thumbnail download/write error handling and clean up the
  .tmp file on a write failure
- tests: upsert/processed write-failure regression tests + split-guard test

apps/trip-cluster/app/routes/review.py

@@ -113,9 +113,8 @@ def apply_one(cid):
     # Lazy import: app.writeback is owned by a later task and may be absent
     # at app-startup; importing here keeps the blueprint importable regardless.
     from app.writeback import apply_cluster
-    s = _store()
-    res = apply_cluster(_client(), s, cid)
-    s.close()
+    with _store() as s:               # close even if the Immich write-back raises
+        res = apply_cluster(_client(), s, cid)
     return jsonify(res)
 
 
@@ -123,7 +122,6 @@ def apply_one(cid):
 def apply_everything():
     # Lazy import: see apply_one above.
     from app.writeback import apply_all
-    s = _store()
-    results = apply_all(_client(), s)
-    s.close()
+    with _store() as s:               # close even if the Immich write-back raises
+        results = apply_all(_client(), s)
     return jsonify({"results": results})