Add Claude Code hooks for automatic CodeGraph sync

PostToolUse(Edit|Write) marks the project dirty via .codegraph/.dirty,
and Stop syncs only if dirty — batching all edits into one sync per
Claude response. The installer now writes these hooks to settings.json.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/directory.ts

@@ -96,6 +96,9 @@ cache/
 
 # Logs
 *.log
+
+# Hook markers
+.dirty
 `;
 
     fs.writeFileSync(gitignorePath, gitignoreContent, 'utf-8');