Enhance hooks with session-start script and documentation

- Add hooks/scripts/session-start.sh that:
  - Checks for unsummarized sessions
  - Checks for pending decisions
  - Outputs context to session
- Update hooks.json to use the script
- Add hooks/README.md documenting hook events and configuration

This provides automatic context loading at session start.

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

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

hooks/hooks.json

@@ -5,7 +5,7 @@
         "hooks": [
           {
             "type": "command",
-            "command": "echo 'SessionStart:Callback hook success: Success'"
+            "command": "~/.claude/hooks/scripts/session-start.sh"
           }
         ]
       }