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/scripts/pre-compact.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+# Pre-compact hook - saves context before compaction
+# Output reminds Claude to summarize important context
+
+set -euo pipefail
+
+echo "PreCompact:Callback hook success: Success"
+echo "PreCompact hook additional context: <EXTREMELY_IMPORTANT>"
+echo "Context compaction is about to occur. Before compacting:"
+echo "1. Note any pending tasks or decisions that need to be preserved"
+echo "2. Summarize key context that should persist"
+echo "3. If working on a multi-step task, note current progress"
+echo "</EXTREMELY_IMPORTANT>"