fix(projekt-matching): final-review fixes — safe redeploy, poison-mail hardening, plan deviations note

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

projekt-matching/projektmatch/mailer.py

@@ -30,6 +30,8 @@ class MailBox:
 
     def fetch(self, uid):
         typ, data = self.conn.uid("FETCH", uid, "(BODY.PEEK[])")
+        if typ != "OK" or not data or not data[0] or not isinstance(data[0], tuple):
+            raise RuntimeError(f"FETCH {uid} fehlgeschlagen: {typ}")
         return email.message_from_bytes(data[0][1], policy=default_policy)
 
     def flag_checked(self, uid):