feat: seed default MCP servers (Findings, SBOM, DAST) on dashboard startup

- Add MCP_ENDPOINT_URL env var to configure MCP server base URL
- Seed three default MCP server configs on dashboard startup if not present
- Each server has its own tool subset: findings (3 tools), SBOM (2 tools), DAST (2 tools)
- Uses upsert-by-name to avoid duplicates on restart

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.env.example

@@ -38,6 +38,9 @@ GIT_CLONE_BASE_PATH=/tmp/compliance-scanner/repos
 DASHBOARD_PORT=8080
 AGENT_API_URL=http://localhost:3001
 
+# MCP Server
+MCP_ENDPOINT_URL=http://localhost:8090
+
 # Keycloak (required for authentication)
 KEYCLOAK_URL=http://localhost:8080
 KEYCLOAK_REALM=compliance