Add self-service password change, forgot-password flow, and fix admin UI bugs

Users can change their own password from the profile modal, and a
"forgot password" link sends a 15-minute expiring reset link (same
hashed-token pattern as site invites). The forgot-password response is
always generic so it never reveals which emails are registered.

Also fixes two admin-page display bugs found while testing: table row
divider lines that didn't line up across a row (the actions column had
`display: flex` on the <td> itself, breaking it out of normal table-cell
layout -- moved to a child <div>), and the pending-invites list floating
with no visual grouping (now boxed with a label and per-status badges).

backend/app/models/__init__.py

@@ -7,6 +7,7 @@ from app.models.membership import RoomMembership, RoomRole
 from app.models.message import Message
 from app.models.message_image import MessageImage
 from app.models.message_reaction import MessageReaction
+from app.models.password_reset import PasswordReset
 from app.models.push_subscription import PushSubscription
 from app.models.room import Room
 from app.models.site_invite import SiteInvite
@@ -24,6 +25,7 @@ __all__ = [
     "MessageImage",
     "MessageReaction",
     "InviteStatus",
+    "PasswordReset",
     "SiteInvite",
     "SmtpSettings",
     "PushSubscription",