feat!: remove the shared demo account

The demo account — one shared user that whitelisted emails entered from
the login page, reset on a schedule — goes end to end (owner decision,
E34): demo.py and the reset job, users.is_demo and demo_whitelist
(migration 0098 deletes the demo user, its audit rows, the reset job's
override and notices, then drops the column and table; the downgrade
restores the empty schema), the /auth/demo entry, the admin whitelist and
reset, the Demo tab, the banner, the login page's "Try the demo", and
every is_demo branch in routes, userscope, scheduler and the UI.

require_human only ever refused the demo account, so its 87 uses become
current_user (owner-approved); require_write_scope keeps its own check.
The login page's "or" divider now shows only beside the Google button:
without the demo entry under it, an instance without Google would have
said "or" to nothing.

A contract test (removedFeatures) fails on the word anywhere in the
backend, frontend, e2e or scripts — seen red on a planted hit. Size
ceilings tightened for the modules that shrank; admin.py is back under
the limit.

backend/app/scheduler.py

@@ -13,9 +13,8 @@ from app import audit, debugsession, logs, logsink, progress, quota
 from app.audit import AuditAction
 from app.config import settings
 from app.db import SessionLocal
-from app.demo import reset_demo_state
 from app.downloads.gc import run_download_gc
-from app.models import SchedulerSetting, User
+from app.models import SchedulerSetting
 from app.plex.sync import sync as run_plex_sync
 from app.plex.tmdb import run_enrich as run_tmdb_enrich
 from app.plex.tmdb import run_people_enrich
@@ -63,7 +62,6 @@ JOB_INTERVALS: dict[str, int] = {
     "subscriptions": settings.subscriptions_resync_minutes,
     "playlist_sync": settings.playlist_sync_minutes,
     "maintenance": settings.maintenance_interval_minutes,
-    "demo_reset": settings.demo_reset_minutes,
     "explore_cleanup": settings.explore_cleanup_minutes,
     "download_gc": settings.download_gc_minutes,
     "plex_sync": settings.plex_sync_interval_min,
@@ -139,8 +137,7 @@ def _notify_done(
 def _run_changed(result) -> bool:
     """Did an automatic job run actually do something worth an audit row? (No-op polls don't.)
     A "change" = a truthy NUMERIC count; status-string dicts like {"skipped": "disabled"} (Plex
-    off — the default) or {"skipped": "no demo account"} are no-ops, not changes, so they don't
-    flood the trail every interval."""
+    off — the default) are no-ops, not changes, so they don't flood the trail every interval."""
     if result is None:
         return False
     if isinstance(result, dict):
@@ -370,17 +367,6 @@ def _maintenance_job() -> None:
     _job("maintenance", work)
 
 
-def _demo_reset_job() -> None:
-    # Auto-clean the shared demo sandbox. No-op (and never creates one) if there's no demo account.
-    def work(db):
-        demo = db.query(User).filter(User.is_demo.is_(True)).one_or_none()
-        if demo is None:
-            return {"skipped": "no demo account"}
-        return {"playlists_seeded": reset_demo_state(db, demo)}
-
-    _job("demo_reset", work)
-
-
 def _explore_cleanup_job() -> None:
     # Reclaim un-kept ephemeral discovery content (explored channels + live-search results) after
     # their grace periods. 0 quota (pure DB), so no quota attribution.
@@ -466,7 +452,6 @@ JOB_FUNCS: dict[str, Callable[[], None]] = {
     "subscriptions": _subscriptions_job,
     "playlist_sync": _playlist_sync_job,
     "maintenance": _maintenance_job,
-    "demo_reset": _demo_reset_job,
     "explore_cleanup": _explore_cleanup_job,
     "download_gc": _download_gc_job,
     "plex_sync": _plex_sync_job,