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/hooks.json

@@ -9,6 +9,16 @@
           }
         ]
       }
+    ],
+    "PreCompact": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "~/.claude/hooks/scripts/pre-compact.sh"
+          }
+        ]
+      }
     ]
   }
 }