Remove Docker support files and documentation

Remove Docker deployment files and all references from README:
- Deleted Dockerfile
- Deleted docker-compose.yml (production)
- Deleted docker-compose.dev.yml (development)
- Removed Docker from Tech Stack section
- Removed Docker Deployment section from README

Docker support may be revisited and added back in the future.
For now, focus is on manual deployment as documented in the
Production Setup Guide.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docker-compose.dev.yml

@@ -1,37 +0,0 @@
-# KeepItGoing - Development Docker Compose Configuration
-# Usage: docker-compose -f docker-compose.dev.yml up -d
-
-version: '3.8'
-
-services:
-  db:
-    image: postgres:16-alpine
-    ports:
-      - "5432:5432"
-    volumes:
-      - postgres_data_dev:/var/lib/postgresql/data
-    environment:
-      POSTGRES_DB: keepitgoing
-      POSTGRES_USER: keepitgoing
-      POSTGRES_PASSWORD: keepitgoing
-    healthcheck:
-      test: ["CMD-SHELL", "pg_isready -U keepitgoing"]
-      interval: 5s
-      timeout: 5s
-      retries: 5
-
-  redis:
-    image: redis:7-alpine
-    ports:
-      - "6379:6379"
-    volumes:
-      - redis_data_dev:/data
-    healthcheck:
-      test: ["CMD", "redis-cli", "ping"]
-      interval: 5s
-      timeout: 5s
-      retries: 5
-
-volumes:
-  postgres_data_dev:
-  redis_data_dev: