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/migrations/versions/0020_system_mail.py

@@ -0,0 +1,48 @@
+"""outgoing system mail (password reset) configured in the admin panel
+
+The server sends its own mail — today only password-reset links — through an
+SMTP account the administrator sets up in the admin panel. The password is
+envelope-encrypted with MASTER_KEY like every mail-account secret. ``public_url``
+is where users reach the app; reset links are built from it, never from the
+request's Host header, which an attacker controls.
+
+Revision ID: 0020
+Revises: 0019
+Create Date: 2026-09-30
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+from alembic import op
+
+revision: str = "0020"
+down_revision: str | None = "0019"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+_COLUMNS = (
+    ("smtp_host", "text NOT NULL DEFAULT ''"),
+    ("smtp_port", "integer NOT NULL DEFAULT 587"),
+    ("smtp_security", "text NOT NULL DEFAULT 'starttls'"),
+    ("smtp_username", "text NOT NULL DEFAULT ''"),
+    ("smtp_secret_ct", "bytea"),
+    ("smtp_from", "text NOT NULL DEFAULT ''"),
+    ("public_url", "text NOT NULL DEFAULT ''"),
+)
+
+
+def upgrade() -> None:
+    for name, ddl in _COLUMNS:
+        op.execute(f"ALTER TABLE app_settings ADD COLUMN {name} {ddl}")
+    op.execute(
+        "ALTER TABLE app_settings ADD CONSTRAINT ck_app_settings_smtp_security "
+        "CHECK (smtp_security IN ('starttls', 'ssl', 'none'))"
+    )
+
+
+def downgrade() -> None:
+    op.execute("ALTER TABLE app_settings DROP CONSTRAINT IF EXISTS ck_app_settings_smtp_security")
+    for name, _ in reversed(_COLUMNS):
+        op.execute(f"ALTER TABLE app_settings DROP COLUMN IF EXISTS {name}")