Add new skills for backend patterns, coding standards, continuous learning, and NestJS best practices

- Introduced backend patterns skill with guidelines on API design, database optimization, and server-side best practices.
- Added coding standards skill outlining universal coding principles for TypeScript, NestJS, and Node.js development.
- Implemented continuous learning skill to automatically extract reusable patterns from Cursor sessions.
- Created NestJS best practices skill detailing architecture patterns, dependency injection, error handling, and security measures.
- Included various rules and templates for NestJS best practices to ensure production-ready applications.

.cursor/commands/refactor-clean.md

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+# Refactor Clean
+
+Safely identify and remove dead code with test verification:
+
+1. Run dead code analysis tools:
+   - knip: Find unused exports and files
+   - depcheck: Find unused dependencies
+   - ts-prune: Find unused TypeScript exports
+
+2. Generate comprehensive report in .reports/dead-code-analysis.md
+
+3. Categorize findings by severity:
+   - SAFE: Test files, unused utilities
+   - CAUTION: API routes, components
+   - DANGER: Config files, main entry points
+
+4. Propose safe deletions only
+
+5. Before each deletion:
+   - Run full test suite
+   - Verify tests pass
+   - Apply change
+   - Re-run tests
+   - Rollback if tests fail
+
+6. Show summary of cleaned items
+
+Never delete code without running tests first!