chore: clean up development artifacts and update .gitignore

- Remove AI agent coordination files and progress tracking
- Remove temporary test results and generated artifacts
- Remove diagnostic test scripts from src/scripts/
- Remove development planning documents
- Update .gitignore to exclude test artifacts
- Clean up 53 temporary files total

.gitignore

@@ -44,12 +44,20 @@ test-reports/
 test-summary.md
 test-metadata.json
 benchmark-results.json
+benchmark-results*.json
+benchmark-summary.json
+coverage-report.json
 benchmark-comparison.md
 benchmark-comparison.json
 benchmark-current.json
 benchmark-baseline.json
 tests/data/*.db
 tests/fixtures/*.tmp
+tests/test-results/
+.test-dbs/
+junit.xml
+*.test.db
+test-*.db
 .vitest/
 
 # TypeScript