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.

.env.example

@@ -0,0 +1,70 @@
+# Momentry Core Configuration Template
+# Copy this file to .env and customize for your environment
+# DO NOT commit .env with real credentials to version control
+
+# ===========================================
+# Database Configuration
+# ===========================================
+DATABASE_URL=postgres://user:password@localhost:5432/momentry
+
+# ===========================================
+# Redis Configuration
+# ===========================================
+REDIS_URL=redis://user:password@localhost:6379
+REDIS_PASSWORD=your_redis_password
+
+# ===========================================
+# MongoDB Configuration
+# ===========================================
+MONGODB_URL=mongodb://user:password@localhost:27017/admin
+MONGODB_DATABASE=momentry
+
+# ===========================================
+# Qdrant Configuration
+# ===========================================
+QDRANT_URL=http://localhost:6333
+QDRANT_API_KEY=your_qdrant_api_key
+QDRANT_COLLECTION=chunks_v3
+
+# ===========================================
+# API Server Configuration
+# ===========================================
+API_HOST=127.0.0.1
+API_PORT=3000
+
+# ===========================================
+# Directory Paths
+# ===========================================
+MOMENTRY_OUTPUT_DIR=/path/to/output
+MOMENTRY_BACKUP_DIR=/path/to/backup
+MOMENTRY_SCRIPTS_DIR=/path/to/momentry_core/scripts
+MOMENTRY_PYTHON_PATH=/opt/homebrew/bin/python3.11
+
+# ===========================================
+# Processor Timeouts (seconds)
+# ===========================================
+MOMENTRY_ASR_TIMEOUT=3600
+MOMENTRY_CUT_TIMEOUT=3600
+MOMENTRY_DEFAULT_TIMEOUT=7200
+
+# ===========================================
+# Watch Directories (comma separated)
+# ===========================================
+WATCH_DIRECTORIES=~/Videos,~/Downloads
+
+# ===========================================
+# Logging
+# ===========================================
+RUST_LOG=info
+# Options: trace, debug, info, warn, error
+
+# ===========================================
+# Ollama (for LLM integration)
+# ===========================================
+OLLAMA_HOST=http://localhost:11434
+
+# ===========================================
+# Model Paths
+# ===========================================
+# EMBEDDING_MODEL_PATH=./models/embedding
+# LLM_MODEL_PATH=./models/llm