feat(ux): R11 feedback symmetry — Plex/download/rollback/deny notices

Give equal-weight actions equal-weight feedback (R11).

S1 Plex error toasts: the watched-toggles (card / season mark-all / episode /
info-panel / show mark-all) used to fail silently on 403/404/429; each now surfaces
the server reason via a shared notifyActionError() + resyncs the optimistic flip.
The playback auto-mark-watched stays intentionally silent (a mid-play toast is
noise; the next sync corrects it). New generic lib/actionErrors.ts (Plex + saved
views reuse it; notifyYouTubeActionError delegates its non-403 case to it).

S2 download-done inbox notification: worker.py emits a best-effort type=download_done
notice to the job owner on real completion (regular + edit jobs, not instant
cache-hits), rendered/localized in the inbox with an Open-Downloads link.

S3 optimistic rollbacks: SavedViewsWidget create/rename/toggle-default/remove/reorder
and the inbox revert-state no longer swallow failures — they toast + refetch to
resync (the reorder's optimistic order reverts to server truth).

S4 access-request deny: deny_invite now emails the requester (send_access_denied),
mirroring approve — no more silent limbo.

backend/app/email.py

@@ -83,6 +83,19 @@ def send_access_approved(email: str) -> bool:
     return _send([email], "You're in — your Siftlode access is approved", body, reply_to=admin)
 
 
+def send_access_denied(email: str) -> bool:
+    admin = _admin_contact()
+    body = (
+        "Hi,\n\n"
+        "Thanks for your interest in Siftlode. After review, your access request wasn't approved "
+        "this time.\n\n"
+        "If you think this was a mistake, you're welcome to reply and let us know.\n\n"
+        "— Siftlode"
+        + (f"\n\nQuestions? Just reply to this email ({admin})." if admin else "")
+    )
+    return _send([email], "About your Siftlode access request", body, reply_to=admin)
+
+
 def send_role_changed(to: str, role: str, operator: str | None) -> bool:
     line = (
         "You've been granted admin access on Siftlode — you can now manage settings, the "

backend/app/routes/admin.py

@@ -105,10 +105,15 @@ def approve_invite(
 @router.post("/invites/{invite_id}/deny")
 def deny_invite(
     invite_id: int,
+    background: BackgroundTasks,
     admin: User = Depends(admin_user),
     db: Session = Depends(get_db),
 ) -> dict:
-    return _serialize(_decide(db, invite_id, admin, approved=False))
+    # Symmetry with approve: the requester hears back either way, instead of a silent limbo. No
+    # account is activated, so this is an email only (the requester has no in-app inbox yet).
+    inv = _decide(db, invite_id, admin, approved=False)
+    background.add_task(email_mod.send_access_denied, inv.email)
+    return _serialize(inv)
 
 
 class AddInviteIn(BaseModel):

backend/app/worker.py

@@ -34,10 +34,31 @@ from app.downloads import edit as editmod
 from app.downloads import errors as dlerrors
 from app.downloads import formats, quota, service, storage
 from app.models import DownloadJob, MediaAsset
+from app.notifications import create_notification
 from app.titles import normalize_title
 
 log = logging.getLogger("siftlode.worker")
 
+
+def _notify_download_done(db, job: DownloadJob | None, title: str | None) -> None:
+    """Post a best-effort 'download ready' notice to the owner's inbox — downloads used to slide to
+    Done silently while scheduler jobs and playlist-push already notified (R11 feedback symmetry).
+    A notification failure must never mask the completed download, so it is isolated + rolled back
+    (mirrors scheduler._notify_done). English title is a fallback; the inbox localizes from `data`."""
+    if not job:
+        return
+    try:
+        create_notification(
+            db,
+            user_id=job.user_id,
+            type="download_done",
+            title=f"Download ready: {title}" if title else "Download ready",
+            data={"title": title},
+        )
+    except Exception:
+        db.rollback()
+        log.exception("failed to write download-done notification for job %s", job.id)
+
 _stop = threading.Event()
 
 
@@ -637,6 +658,7 @@ def _download(job_id: int, asset_id: int, source_kind: str, source_ref: str, spe
                     # display_name is VARCHAR(255) — clip a long title (see _fill_asset_meta_early).
                     job.display_name = meta.title[:255] if meta.title else None
             db.commit()
+            _notify_download_done(db, job, meta.title)
         log.info("job %s done: %s", job_id, rel)
 
     except (_Aborted, editmod.EditAborted):
@@ -769,6 +791,7 @@ def _process_edit(job_id: int, asset_id: int) -> None:
                 job.progress = 100
                 job.phase = None
             db.commit()
+            _notify_download_done(db, job, asset.title if asset else None)
         log.info("edit job %s done: %s", job_id, rel)
 
     except editmod.EditAborted: