Add dedup_review_service and genre_review_service

dedup-library.sh: additive --json (one NDJSON line per candidate deletion
to stdout, alongside the unchanged human log) and --only-paths FILE (in
--apply mode, only actually delete entries whose path is in FILE; without
it, --apply deletes everything as before -- existing direct callers are
unaffected). Without --only-paths the safety re-verification is free:
--apply --only-paths re-runs all 4 passes from scratch on every invocation,
so if a group's ranking changed since a scan (e.g. the old keep_path is
gone), the fresh pass assigns the previously-"delete" path the KEEP role
instead and the only-paths allowlist naming it is simply never consulted --
no duplicate ranking logic needed in the review service.

spotify-genre.py: additive --json emitting one JSON line per genre change
(dry-run or --apply) for genre_review_service to persist.

pipeline_runner.run_job_capture(): like run_job() but captures stdout as
text (still under the same shared lock, still writes a job_runs row) for
callers that need to parse structured output rather than just log it.

dedup_review_service.scan() persists dry-run candidates into
dedup_runs/dedup_candidates. confirm_and_apply() re-checks confirmed
candidates still exist before invoking --apply --only-paths, so nothing is
ever deleted without an explicit confirm -- matches the false-negative-
biased dedup preference. scheduler_service's maintenance:dedup job now
goes through this (still dry-run only, every day).

genre_review_service.run() wraps spotify-genre.py for both dry-run preview
and the real scheduled --apply run, persisting every run's diff into
genre_runs/genre_candidates either way -- genre writes keep their current
auto-apply behavior (low-risk, reversible, GENRE_LOCK-protected) but are
now reviewable after the fact. lock_artist_genre() gives a one-click revert
path when a run gets something wrong.

Added minimal routers+templates for /dedup (scan, review, confirm-and-
delete) and /genres (preview, review, lock-old-genre).

Verified end-to-end against REAL duplicate files (not mocked): built an
actual FLAC+MP3 duplicate pair in a real beets library, ran dedup-library.sh
--json and confirmed correct JSON output, verified --apply --only-paths
with an empty confirm list deletes nothing and with the real confirmed path
deletes exactly that file (DB + disk) while preserving the FLAC, and ran
the full dedup_review_service scan->confirm->apply flow through the same
fixture. genre_review_service and spotify-genre.py --json verified against
mocked/direct output (spotify-genre.py's own artist-genre lookup needs a
live Spotify API call, out of reach in this sandbox). Confirmed the full
app boots with all five routers registered.

pipeline/lib/spotify-genre.py

@@ -277,6 +277,10 @@ def main():
                     help="Overwrite existing GENRE tags (default: only fill empty)")
     ap.add_argument("--query", help="Beets query to limit which tracks are processed")
     ap.add_argument("--limit", type=int, help="Stop after N tracks (debug)")
+    ap.add_argument("--json", action="store_true",
+                    help="Additionally emit one JSON line per candidate change to stdout, "
+                         "for genre_review_service to parse into genre_runs/genre_candidates. "
+                         "Purely additive -- normal output is unchanged.")
     args = ap.parse_args()
 
     whitelist = load_whitelist()
@@ -333,11 +337,21 @@ def main():
             ok = write_genre(p, new_value)
             if ok:
                 written += 1
+                if args.json:
+                    print(json.dumps({
+                        "artist": primary_artist, "title": title,
+                        "old_genre": current_genre, "new_genre": new_value,
+                    }))
                 # Quiet — only print every 50th
                 if written % 50 == 0:
                     print(f"  [{written}] {primary_artist} - {title}: {new_value}", flush=True)
         else:
             print(f"  WOULD-SET {primary_artist} - {title}  →  {new_value}")
+            if args.json:
+                print(json.dumps({
+                    "artist": primary_artist, "title": title,
+                    "old_genre": current_genre, "new_genre": new_value,
+                }))
             written += 1  # count as 'planned'
 
     print(f"\n[spotify-genre] {('written' if args.apply else 'plan')}: {written}, "