Configure the invitation mailbox in the UI, not the environment

Putting IMAP settings in environment variables was my call to make and it was
the wrong one: it meant editing a file on the server and restarting to change a
folder name, and it was never offered as a choice.

The mailbox is now a row in mailbox_accounts, edited under Settings → Admin:
host, user, password, port, folder, interval, on/off. Administrators only — it
is a shared forwarding target, not a per-user account. The password is never
returned by any endpoint, the same as the CalDAV account routes, and leaving
the field empty on edit keeps the stored one so changing a port does not mean
retyping it. The panel shows when the mailbox was last read and what went wrong
if it did, because a mailbox that quietly stopped working looks exactly like
one that has no mail.

Worth stating plainly: the password now lives in the database, in clear text,
like the CalDAV, Google and Home Assistant credentials beside it. Unlike those
three, an IMAP password opens an entire mailbox.

The scheduler job is registered unconditionally now — whether a mailbox exists
can change without a restart, and fetch_invites returns immediately when none
does. test_scheduler knows about it.

Also adds the requests list to the sidebar with accept and decline, 26
translation keys across all ten languages, and tests covering that the password
is never returned, that an edit without one keeps it, and that a disabled
mailbox counts as unconfigured.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/mail_invites.py

@@ -6,9 +6,10 @@ mail can only ever create a row in ``event_invites``. No calendar read path
 touches that table — an invitation becomes an event when a human accepts it, and
 not before.
 
-Credentials live in the environment, never in the database. The service already
-loads an EnvironmentFile, and this keeps the one secret that grants access to a
-whole mailbox out of a table that an endpoint could return.
+The mailbox is configured in the UI and stored in ``mailbox_accounts`` — one row
+per instance, since it is a shared forwarding target rather than a per-user
+account. The password is kept as given, like every other external account here;
+no endpoint returns it.
 
 Single process assumed, same as the rest of the scheduler (see scheduler.py).
 """
@@ -18,7 +19,6 @@ from __future__ import annotations
 import contextlib
 import imaplib
 import logging
-import os
 import re
 import uuid
 from datetime import datetime, timezone
@@ -49,8 +49,15 @@ _ADDR_RE = re.compile(r"^[^@\s<>\",;:]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$")
 _HANDLED_METHODS = ("REQUEST", "CANCEL")
 
 
-def is_configured() -> bool:
-    return bool(os.environ.get("IMAP_HOST"))
+def get_account(db: Session):
+    """The configured mailbox, or None. Disabled counts as not configured."""
+    return (db.query(models.MailboxAccount)
+              .filter(models.MailboxAccount.enabled.is_(True))
+              .order_by(models.MailboxAccount.id).first())
+
+
+def is_configured(db: Session) -> bool:
+    return get_account(db) is not None
 
 
 def _valid_address(addr: str | None) -> str | None:
@@ -193,13 +200,10 @@ def ingest_ics(db: Session, raw: bytes) -> bool:
 # ── Mailbox ───────────────────────────────────────────────
 
 
-def _connect() -> imaplib.IMAP4:
-    host = os.environ["IMAP_HOST"]
-    port = int(os.environ.get("IMAP_PORT", "993"))
-    use_ssl = os.environ.get("IMAP_SSL", "1") != "0"
-    box = (imaplib.IMAP4_SSL(host, port, timeout=30) if use_ssl
-           else imaplib.IMAP4(host, port, timeout=30))
-    box.login(os.environ["IMAP_USER"], os.environ["IMAP_PASSWORD"])
+def _connect(acc) -> imaplib.IMAP4:
+    box = (imaplib.IMAP4_SSL(acc.imap_host, acc.imap_port, timeout=30) if acc.imap_ssl
+           else imaplib.IMAP4(acc.imap_host, acc.imap_port, timeout=30))
+    box.login(acc.imap_user, acc.imap_password)
     return box
 
 
@@ -246,12 +250,29 @@ def _handle_message(db: Session, box: imaplib.IMAP4, uid: bytes) -> None:
 
 
 def fetch_invites(db: Session) -> None:
-    """Scheduler job: read new mail and store any invitations it holds."""
-    if not is_configured():
+    """Scheduler job: read new mail and store any invitations it holds.
+
+    Records what happened on the account so the UI can show a mailbox that
+    stopped working, rather than letting invitations quietly never arrive.
+    """
+    acc = get_account(db)
+    if acc is None:
         return
-    box = _connect()
     try:
-        box.select(os.environ.get("IMAP_FOLDER", "INBOX"))
+        _run(db, acc)
+        acc.last_error = None
+    except Exception as exc:
+        logger.exception("Postfach %s nicht erreichbar", acc.imap_host)
+        acc.last_error = f"{type(exc).__name__}: {exc}"[:500]
+    acc.last_run = datetime.now(timezone.utc)
+    with contextlib.suppress(Exception):
+        db.commit()
+
+
+def _run(db: Session, acc) -> None:
+    box = _connect(acc)
+    try:
+        box.select(acc.imap_folder or "INBOX")
         # UID commands, not sequence numbers: those shift when a message is
         # expunged mid-run and we would read the wrong mail.
         typ, data = box.uid("SEARCH", None, "UNSEEN")