calendar-invite: strip METHOD from ICS before CalDAV storage

CalDAV servers (Migadu) reject ICS files with METHOD:REQUEST/REPLY
as it's an iTIP email concept, not a storage property. Strip it
when saving to local calendar, for both send and reply flows.

skills/calendar-invite/scripts/calendar_invite.py

@@ -74,6 +74,17 @@ def _build_calendar_email(from_addr, to_addr, subject, body, ics_bytes, method="
     return msg.as_string()
 
 
+def _strip_method(ics_bytes):
+    """Remove METHOD property from ICS for CalDAV storage.
+
+    CalDAV servers reject METHOD (it's an iTIP/email concept, not a storage one).
+    """
+    cal = Calendar.from_ical(ics_bytes)
+    if "method" in cal:
+        del cal["method"]
+    return cal.to_ical()
+
+
 def _parse_iso_datetime(dt_str):
     """Parse ISO 8601 datetime string to a datetime object."""
     # Handle both 2026-03-20T14:00:00 and 2026-03-20T14:00
@@ -167,10 +178,10 @@ def cmd_send(args):
     _send_email(email_str, args.account)
     print(f"Calendar invite sent to: {args.to}")
 
-    # Save to local calendar
+    # Save to local calendar (without METHOD for CalDAV compatibility)
     if CALENDAR_DIR.is_dir():
         dest = CALENDAR_DIR / f"{uid}.ics"
-        dest.write_bytes(ics_bytes)
+        dest.write_bytes(_strip_method(ics_bytes))
         print(f"Saved to local calendar: {dest}")
         _sync_calendar()
 
@@ -344,8 +355,8 @@ def cmd_reply(args):
     if CALENDAR_DIR.is_dir():
         dest = CALENDAR_DIR / f"{uid}.ics"
         if partstat in ("ACCEPTED", "TENTATIVE"):
-            # Save the original event to local calendar
-            dest.write_bytes(ics_path.read_bytes())
+            # Save the original event to local calendar (without METHOD for CalDAV)
+            dest.write_bytes(_strip_method(ics_path.read_bytes()))
             print(f"Saved to local calendar: {dest}")
         elif partstat == "DECLINED" and dest.is_file():
             dest.unlink()