Admin user management, password reset by email, and the Ultimo Email name

Branding: the page titles and app name are now "Ultimo Email".

Admin panel (now two columns with a divider):
- Users: search by login or by a mail account's address or name (results
  only, nothing listed until something is typed). A user opens a window to
  change their quota, block/unblock them, or delete them; block and delete ask
  for confirmation, and an admin cannot do either to their own account.
- Blocking (users.blocked_at, migration 0019) refuses sign-in with a clear
  message and revokes every session; a new user.signed_out event sends the
  user's open tabs to the sign-in screen at once. Any "not signed in" answer
  now does the same, not only /auth/me. Deleting removes mail accounts (sync
  stops), plugin rows (cleared inside the user's RLS context, since plugin
  tables have no FK to users), blobs, the search index, sessions and the user.
- Outgoing system mail (migration 0020): SMTP server, port, security, login,
  password (vault-encrypted, never sent back), From address and the public
  address reset links point to, plus a "Send test" that reports the server's
  error.

Password reset:
- "Forgot password?" on the sign-in page asks for the user name and always
  answers "If this account exists you will receive an email to your recovery
  email address"; the mail goes out after the response, so neither the reply
  nor its timing reveals an account, and it is capped at 3 per hour.
- The emailed link (token in the URL fragment, single use, 30 minutes) opens a
  page to set a new password. With 2-step verification on, the code is checked
  before anything changes; five wrong codes burn the link.
- Settings > Profile: the recovery email can be added, changed or removed,
  confirmed with the current password, which must be typed — autofill and
  paste are refused (TypedPasswordInput).

Also adds frontend/icons/ultimo-logo-bimi.svg, an SVG Tiny PS version of the
logo for a BIMI record.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/app/models.py

@@ -69,6 +69,19 @@ class AppSettings(Base):
     default_quota_bytes: Mapped[int] = mapped_column(
         BigInteger, nullable=False, server_default=text("5368709120")
     )
+    # Outgoing system mail (password-reset links): the SMTP account the server
+    # sends from. The password is vault-encrypted (like Account.secret_ct).
+    smtp_host: Mapped[str] = mapped_column(Text, nullable=False, server_default=text("''"))
+    smtp_port: Mapped[int] = mapped_column(Integer, nullable=False, server_default=text("587"))
+    smtp_security: Mapped[str] = mapped_column(
+        Text, nullable=False, server_default=text("'starttls'")
+    )  # starttls | ssl | none
+    smtp_username: Mapped[str] = mapped_column(Text, nullable=False, server_default=text("''"))
+    smtp_secret_ct: Mapped[bytes | None] = mapped_column(BYTEA)
+    smtp_from: Mapped[str] = mapped_column(Text, nullable=False, server_default=text("''"))
+    # Where users reach the app, e.g. https://mail.example.com — reset links are
+    # built from this, never from the request's Host header.
+    public_url: Mapped[str] = mapped_column(Text, nullable=False, server_default=text("''"))
     updated_at: Mapped[dt.datetime] = _now()
 
 
@@ -91,6 +104,9 @@ class User(Base):
     # The first account created on a fresh install bootstraps as administrator;
     # the admin panel can grant it to others later.
     is_admin: Mapped[bool] = mapped_column(nullable=False, server_default=text("false"))
+    # Set while an administrator has blocked the account (no sign-in, sessions
+    # refused); NULL when not blocked.
+    blocked_at: Mapped[dt.datetime | None] = mapped_column(TIMESTAMP(timezone=True))
     created_at: Mapped[dt.datetime] = _now()