perf: optimize drawings endpoint with caching and lazy loading

- Add 5s in-memory cache for /drawings responses with automatic cleanup
- Split Drawing/DrawingSummary types for efficient data fetching
- Implement lazy loading of drawing data in DrawingCard component
- Add configurable DRAWINGS_CACHE_TTL_MS and RATE_LIMIT_MAX_REQUESTS env vars
- Prevent memory leaks with periodic cleanup of cache and rate limit maps
- Add loading states and better UX for export operations
- Improve JSON parsing with error handling for malformed stored data

Benchmark results (100 drawings, cached):
- Avg latency: 6.94ms (p50: 4ms, p97.5: 8ms)
- Avg throughput: 668 req/s (peak: 1,023)
- 3k requests in 5s with 0 errors

Update .gitignore to exclude generated files, env files, and build artifacts

.gitignore

@@ -1,3 +1,76 @@
+# Dependencies
 frontend/node_modules
+backend/node_modules
+
+# Database
+backend/prisma/*.db
+backend/prisma/dev.db
+
+# Generated files
+backend/src/generated/
+
+# Environment variables
+.env
+.env.local
+.env.production
+.env.staging
+
+# Build outputs
+frontend/dist/
+frontend/build/
+backend/dist/
+
+# Logs
+*.log
+logs/
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# Runtime data
+pids
+*.pid
+*.seed
+*.pid.lock
+
+# Coverage directory used by tools like istanbul
+coverage/
+*.lcov
+
+# Dependency directories
+jspm_packages/
+
+# Optional npm cache directory
+.npm
+
+# Optional REPL history
+.node_repl_history
+
+# Output of 'npm pack'
+*.tgz
+
+# Yarn Integrity file
+.yarn-integrity
+
+# dotenv environment variables file
+.env.test
+
+# IDE/Editor files
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# OS generated files
 .DS_Store
-backend/prisma/*.db
+.DS_Store?
+._*
+.Spotlight-V100
+.Trashes
+ehthumbs.db
+Thumbs.db
+
+# Temporary files
+*.tmp
+*.temp