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>

hooks/README.md

@@ -7,6 +7,7 @@ Event handlers that run automatically during Claude Code sessions.
 | Event | Script | Purpose |
 |-------|--------|---------|
 | `SessionStart` | `scripts/session-start.sh` | Load context, check for pending items |
+| `PreCompact` | `scripts/pre-compact.sh` | Remind to preserve context before compaction |
 
 ## Hook Events