calendar-invite: add VALARM reminder, fix terminology, remove dead code

- Add 1-day reminder (VALARM) to all sent invites
- Fix datetime.utcnow() deprecation → datetime.now(timezone.utc)
- Rename "message ID" → "envelope ID" in SKILL.md for consistency
- Remove unused _himalaya() and _himalaya_with_account() helpers

skills/calendar-invite/scripts/calendar_invite.py

@@ -14,14 +14,14 @@ import argparse
 import subprocess
 import sys
 import uuid
-from datetime import datetime
+from datetime import datetime, timedelta, timezone
 from pathlib import Path
 
 from email.mime.base import MIMEBase
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
 
-from icalendar import Calendar, Event, vCalAddress, vText
+from icalendar import Alarm, Calendar, Event, vCalAddress, vText
 
 # ---------------------------------------------------------------------------
 # Config
@@ -38,24 +38,6 @@ PRODID = "-//OpenClaw//CalendarInvite//EN"
 # Helpers
 # ---------------------------------------------------------------------------
 
-def _himalaya(*args):
-    """Run a himalaya command and return stdout."""
-    result = subprocess.run(
-        ["himalaya", *args],
-        capture_output=True, text=True, check=True,
-    )
-    return result.stdout
-
-
-def _himalaya_with_account(account, *args):
-    """Run a himalaya command with optional account flag."""
-    cmd = ["himalaya"]
-    if account:
-        cmd += ["--account", account]
-    cmd += list(args)
-    result = subprocess.run(cmd, capture_output=True, text=True, check=True)
-    return result.stdout
-
 
 def _sync_calendar():
     """Sync local calendar to CalDAV server via vdirsyncer."""
@@ -123,7 +105,7 @@ def cmd_send(args):
 
     event = Event()
     event.add("uid", uid)
-    event.add("dtstamp", datetime.utcnow())
+    event.add("dtstamp", datetime.now(timezone.utc))
     event.add("dtstart", start, parameters={"TZID": args.timezone})
     event.add("dtend", end, parameters={"TZID": args.timezone})
     event.add("summary", args.summary)
@@ -151,6 +133,13 @@ def cmd_send(args):
             "RSVP": "TRUE",
         })
 
+    # 1-day reminder
+    alarm = Alarm()
+    alarm.add("action", "DISPLAY")
+    alarm.add("description", f"Reminder: {args.summary}")
+    alarm.add("trigger", timedelta(days=-1))
+    event.add_component(alarm)
+
     cal.add_component(event)
     ics_bytes = cal.to_ical()
 
@@ -286,7 +275,7 @@ def cmd_reply(args):
 
     reply_event = Event()
     reply_event.add("uid", uid)
-    reply_event.add("dtstamp", datetime.utcnow())
+    reply_event.add("dtstamp", datetime.now(timezone.utc))
 
     # Copy timing from original
     if original_event.get("dtstart"):