test: refactor integration tests to use daemon commands

Update integration_test.sh to use new daemon management commands
instead of manual background processes and PIDs:
- Replace `kvs config.yaml &` with `kvs start config.yaml`
- Replace `kill $pid` with `kvs stop config.yaml`
- Update log file paths to use ~/.kvs/logs/
- Add integration_test/ directory to gitignore

All tests now use clean daemon lifecycle management.

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

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

.gitignore

@@ -2,6 +2,7 @@
 .kvs/
 data/
 data*/
+integration_test/
 *.yaml
 !config.yaml
 kvs