Add documentation, PreCompact hook, gcal improvements, and marketplace

Documentation:
- Add commands/README.md documenting all slash commands
- Add skills/README.md documenting skill structure and patterns
- Add .claude-plugin/marketplace.json for local dev testing

Hooks:
- Add PreCompact hook to remind about context preservation
- Update hooks/README.md with new hook

GCal improvements:
- Add scripts/next_event.py for single event lookup
- Update SKILL.md with simplified format and allowed-tools: Read

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

skills/gcal/scripts/next_event.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+"""Get the next upcoming calendar event."""
+import os
+from datetime import datetime
+
+# Set credentials path
+os.environ.setdefault('GMAIL_CREDENTIALS_PATH', os.path.expanduser('~/.gmail-mcp/credentials.json'))
+
+from gmail_mcp.utils.GCP.gmail_auth import get_calendar_service
+
+
+def format_event(event):
+    """Format a single event for display."""
+    start = event['start'].get('dateTime', event['start'].get('date'))
+
+    if 'T' in start:
+        start_dt = datetime.fromisoformat(start.replace('Z', '+00:00'))
+        time_str = start_dt.strftime('%I:%M %p').lstrip('0')
+        date_str = start_dt.strftime('%A, %b %d')
+    else:
+        time_str = "All day"
+        date_str = start
+
+    summary = event.get('summary', '(No title)')
+    location = event.get('location', '')
+
+    print(f"📅 Next Event — {date_str}")
+    print()
+    print(f"  {time_str}   {summary}")
+    if location:
+        print(f"            📍 {location}")
+
+    # Show attendees if available
+    attendees = event.get('attendees', [])
+    if attendees:
+        print(f"            👥 {len(attendees)} attendees")
+
+
+def main():
+    service = get_calendar_service()
+    now = datetime.utcnow().isoformat() + 'Z'
+
+    events_result = service.events().list(
+        calendarId='primary',
+        timeMin=now,
+        maxResults=1,
+        singleEvents=True,
+        orderBy='startTime'
+    ).execute()
+
+    events = events_result.get('items', [])
+
+    if not events:
+        print("📅 No upcoming events")
+        return
+
+    format_event(events[0])
+
+
+if __name__ == '__main__':
+    main()