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.development

@@ -0,0 +1,55 @@
+# Development Environment Configuration
+# Used by: momentry_playground binary
+# 
+# This file is loaded BEFORE the main .env file
+# Settings here override defaults but can be overridden by CLI flags
+
+# Server Configuration
+MOMENTRY_SERVER_PORT=3003
+MOMENTRY_REDIS_PREFIX=momentry_dev:
+
+# Worker Configuration (disabled by default for development)
+MOMENTRY_WORKER_ENABLED=false
+MOMENTRY_MAX_CONCURRENT=1
+MOMENTRY_POLL_INTERVAL=10
+MOMENTRY_WORKER_BATCH_SIZE=5
+
+# Database (same as production, but could use separate dev database)
+DATABASE_URL=postgres://accusys@localhost:5432/momentry
+
+# MongoDB
+MONGODB_URL=mongodb://accusys:Test3200Test3200@localhost:27017/admin
+MONGODB_DATABASE=momentry
+
+# Redis
+REDIS_URL=redis://:accusys@localhost:6379
+REDIS_PASSWORD=accusys
+
+# Paths
+MOMENTRY_OUTPUT_DIR=/Users/accusys/momentry/output_dev
+MOMENTRY_BACKUP_DIR=/Users/accusys/momentry/backup/momentry_dev
+
+# Python (for processing scripts)
+MOMENTRY_PYTHON_PATH=/opt/homebrew/bin/python3.11
+MOMENTRY_SCRIPTS_DIR=/Users/accusys/momentry_core_0.1/scripts
+
+# Logging
+RUST_LOG=debug
+MOMENTRY_LOG_LEVEL=debug
+
+# Media
+MOMENTRY_MEDIA_BASE_URL=https://wp.momentry.ddns.net
+
+# Processor Timeouts
+MOMENTRY_ASR_TIMEOUT=3600
+MOMENTRY_CUT_TIMEOUT=3600
+MOMENTRY_DEFAULT_TIMEOUT=7200
+
+# Cache Settings
+MONGODB_CACHE_ENABLED=true
+MONGODB_CACHE_TTL_VIDEOS=300
+MONGODB_CACHE_TTL_SEARCH=300
+MONGODB_CACHE_TTL_HYBRID_SEARCH=600
+MONGODB_CACHE_TTL_VIDEO_META=3600
+REDIS_CACHE_TTL_HEALTH=30
+REDIS_CACHE_TTL_VIDEO_META=3600