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/routes/discover.py

@@ -17,7 +17,7 @@ from sqlalchemy import select
 from sqlalchemy.exc import IntegrityError
 from sqlalchemy.orm import Session
 
-from app.auth import current_user, require_human
+from app.auth import current_user
 from app.db import get_db
 from app.discover import hero as hero_mod
 from app.discover import pins, rails
@@ -127,15 +127,14 @@ def list_pins(
 @router.post("/pins")
 def add_pin(
     body: PinIn,
-    user: User = Depends(require_human),
+    user: User = Depends(current_user),
     db: Session = Depends(get_db),
 ) -> dict:
     """Pin something to the comfort shelf.
 
-    `require_human`, like every other personal-state write: the shared demo account must not be able
-    to curate a communal shelf. Re-pinning something already on the shelf is a no-op that returns the
-    existing pin rather than a 409 — the gesture is "make sure this is on my shelf", and the unique
-    constraint is the mechanism, not the message."""
+    Re-pinning something already on the shelf is a no-op that returns the existing pin rather than
+    a 409 — the gesture is "make sure this is on my shelf", and the unique constraint is the
+    mechanism, not the message."""
     resolved = pins.resolve_ref(db, user, body.kind, body.ref)
     if resolved is None:
         raise not_found("item")
@@ -178,7 +177,7 @@ def add_pin(
 @router.delete("/pins/{pin_id}")
 def remove_pin(
     pin_id: int,
-    user: User = Depends(require_human),
+    user: User = Depends(current_user),
     db: Session = Depends(get_db),
 ) -> dict:
     pin = owned_or_404(db, ComfortPin, pin_id, user, what="pin")
@@ -190,7 +189,7 @@ def remove_pin(
 @router.post("/pins/reorder")
 def reorder_pins(
     body: ReorderIn,
-    user: User = Depends(require_human),
+    user: User = Depends(current_user),
     db: Session = Depends(get_db),
 ) -> dict:
     """Rewrite the shelf order from the list of pin ids the client shows.