feat: add momentry_playground binary for development

- Add separate momentry_playground binary with distinct configuration
- Production (momentry): Port 3002, Redis prefix 'momentry:'
- Development (momentry_playground): Port 3003, Redis prefix 'momentry_dev:'
- Add SERVER_PORT and REDIS_KEY_PREFIX config via environment variables
- Replace all hardcoded Redis key prefixes with configurable values
- Create .env.development for playground environment settings
- Update .env with production defaults
- Add dotenv dependency for environment file loading

Configuration isolation allows running both binaries simultaneously
without port conflicts or Redis key collisions.

.gitignore

@@ -1,11 +1,40 @@
+# Environment - Local configs (NEVER commit these)
 .env
 .env.local
+.env.*.local
+
+# Build artifacts
 target/
 venv/
+
+# Generated files
 thumbnails/
 *.asr.json
 *.probe.json
 test_asr.json
-.DS_Store
-*.log
+
+# Local output (machine learning results)
+output/
+*.pt
+
+# Cache
 .ruff_cache/
+
+# OS files
+.DS_Store
+.Spotlight-V100
+.Trashes
+
+# Logs
+*.log
+
+# SSH keys (NEVER commit)
+id_*
+!id_*.pub
+
+# IDE and editor
+.vscode/
+.idea/
+*.swp
+*.swo
+*~