detect attachments without Content-Disposition: attachment header

The cps datensysteme rule (from cps-datensysteme.de + subject "Rechnung"
+ has_attachment true + date after) was failing on real invoices from
CPS ORMS. Their PDFs arrive without a Content-Disposition header — the
filename lives only on the Content-Type parameter — so _has_attachment
returned False and the rule never matched.

Extended the check to also count a part as an attachment when it has a
filename() and its content-type is neither text/* nor multipart/*.
That catches PDFs, Office and image attachments regardless of whether
the sender set Content-Disposition, without treating body parts as
attachments. Verified against four synthetic cases including the exact
CPS ORMS shape.

Same helper is now applied to non-multipart mails too, in case an entire
mail is a single attached file (rare but possible).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/services/imap_client.py

@@ -79,13 +79,32 @@ def _parse_date(msg: Message) -> datetime | None:
 
 
 def _has_attachment(msg: Message) -> bool:
-    if not msg.is_multipart():
-        return False
-    for part in msg.walk():
-        disposition = str(part.get("Content-Disposition") or "")
+    """Erkennt Anhänge robuster als nur per Content-Disposition: attachment.
+    Manche Absender (z.B. CPS ORMS) hängen PDFs an, ohne diesen Header zu setzen —
+    der Dateiname steckt dann nur im filename-Parameter. Zusätzliches Kriterium:
+    ein Part, der einen Dateinamen hat UND kein reiner Text- oder Multipart-Container
+    ist, wird als Anhang gewertet. Damit werden PDF/Office/Bilder-Anhänge sicher
+    erkannt, ohne dass Inline-CSS oder HTML-Body fälschlich als Anhang zählt."""
+    def _is_attachment_part(part: Message) -> bool:
+        disposition = str(part.get("Content-Disposition") or "").lower()
         if "attachment" in disposition:
             return True
-    return False
+        filename = part.get_filename()
+        if not filename:
+            return False
+        ctype = (part.get_content_type() or "").lower()
+        # text/* und multipart/* sind normalerweise Body-Teile, keine Anhänge
+        if ctype.startswith("text/") or ctype.startswith("multipart/"):
+            return False
+        return True
+
+    if msg.is_multipart():
+        for part in msg.walk():
+            if _is_attachment_part(part):
+                return True
+        return False
+    # Single-part Mail kann auch ein Anhang sein (selten, aber möglich)
+    return _is_attachment_part(msg)
 
 
 def _extract_body(msg: Message) -> str: