Dedup page: shorten paths, fix column alignment, per-row delete

- Strip the common /data/music/Library/ prefix from displayed keep/delete
  paths (every track lives there, so it added width without adding
  information); full path is still available via a hover title.
- Table now uses a colgroup with fixed column widths so headers stay
  aligned with their content regardless of how long a given path is,
  instead of drifting with the widest cell in the column.
- Add a per-row Delete button (self-contained form per cell) alongside
  the existing checkbox + bulk "Delete selected" flow -- the checkboxes
  now target an external form via the HTML `form` attribute instead of
  wrapping the table in a form, since a form can't legally nest another
  form for the per-row buttons.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/routers/dedup.py

@@ -4,14 +4,35 @@ from fastapi.templating import Jinja2Templates
 
 from app.security.deps import require_auth
 from app.services import dedup_review_service
+from app.settings import settings
 
 router = APIRouter(prefix="/dedup", tags=["dedup"])
 templates = Jinja2Templates(directory="app/templates")
 
+# Every library track lives under this prefix -- showing it on every row of
+# every candidate adds nothing but width, so strip it for display (the full
+# path is still available in the title attribute on hover).
+_LIBRARY_PREFIX = str(settings.music_data_dir / "Library") + "/"
+
+
+def _display_path(path: str) -> str:
+    return path[len(_LIBRARY_PREFIX):] if path.startswith(_LIBRARY_PREFIX) else path
+
 
 @router.get("")
 async def dedup_index(request: Request, user: dict = Depends(require_auth)):
-    candidates = dedup_review_service.list_pending_candidates()
+    candidates = [
+        {
+            "id": c.id,
+            "pass_name": c.pass_name,
+            "keep_path": c.keep_path,
+            "delete_path": c.delete_path,
+            "keep_display": _display_path(c.keep_path),
+            "delete_display": _display_path(c.delete_path),
+            "delete_size_bytes": c.delete_size_bytes,
+        }
+        for c in dedup_review_service.list_pending_candidates()
+    ]
     return templates.TemplateResponse(request, "dedup/index.html", {"candidates": candidates})