Standardize database naming and fix environment configuration

- Renamed database from 'decision_tree' to 'apoklisis' for consistency
- Updated docker-compose.yml: container renamed to 'apoklisis_postgres'
- Updated .env file with correct database URL
- Verified backend authentication flow working correctly
- Added postgres MCP server to Claude Code configuration

backend/.claude/settings.local.json

@@ -0,0 +1,7 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(test:*)"
+    ]
+  }
+}