Initial commit: CodiMD Docker deployment with security hardening

- Add docker-compose.yml with PostgreSQL and CodiMD services
- Add .env.example for environment configuration template
- Add .gitignore to exclude sensitive data and persisted volumes
- Add CLAUDE.md documentation for deployment guidance
- Security hardening: read-only containers, health checks, network isolation

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,10 @@
+# Database Configuration
+POSTGRES_USER=codimd
+POSTGRES_PASSWORD=CHANGE_THIS_TO_A_STRONG_PASSWORD
+POSTGRES_DB=codimd
+
+# CodiMD Configuration
+CMD_DB_URL=postgres://codimd:CHANGE_THIS_TO_A_STRONG_PASSWORD@database/codimd
+
+# CodiMD Session Secret (generate a random string)
+CMD_SESSION_SECRET=CHANGE_THIS_TO_A_RANDOM_SECRET_STRING