fix(mailparser): Deutsche Wochentagsabkürzungen im Date-Header parsen

PMG mit German-Locale erzeugt "So, 24 Aug 2025 00:05:17 +0200" statt
"Sun, ..." — Go's net/mail und alle bisherigen Fallbacks scheitern daran.
Fix: Wochentag-Präfix (≤3 Zeichen vor dem ersten Komma) abschneiden
und erneut mit den numerischen Offset-Formaten parsen.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pkg/mailparser/parser.go

@@ -136,6 +136,30 @@ func Parse(raw []byte) (*ParsedMail, error) {
 				break
 			}
 		}
+		if !parsed {
+			// Some MTAs (e.g. PMG with German locale) use localised weekday names:
+			// "So, 24 Aug 2025 00:05:17 +0200" instead of "Sun, 24 Aug 2025...".
+			// Strip the "Weekday, " prefix (≤3 chars before the first comma) and retry.
+			if commaIdx := strings.Index(raw, ","); commaIdx > 0 && commaIdx <= 3 {
+				noWeekday := strings.TrimSpace(raw[commaIdx+1:])
+				for _, layout := range []string{
+					"2 Jan 2006 15:04:05 -0700",
+					"02 Jan 2006 15:04:05 -0700",
+					"2 Jan 2006 15:04:05 -07:00",
+					"02 Jan 2006 15:04:05 -07:00",
+					"2 Jan 2006 15:04:05 MST",
+					"02 Jan 2006 15:04:05 MST",
+					"2 Jan 2006 15:04 -0700",
+					"02 Jan 2006 15:04 -0700",
+				} {
+					if t, err := time.Parse(layout, noWeekday); err == nil {
+						pm.Date = t
+						parsed = true
+						break
+					}
+				}
+			}
+		}
 		if !parsed {
 			// Leave pm.Date as zero — storage will use DB DEFAULT NOW()
 			pm.Date = time.Time{}