#18 Cockpit API foundation and read-only security

## What to build Establish the versioned, read-only foundation for the city life-line cockpit backend. ## Acceptance criteria - [ ] Schema/DTO defines the AjaxResult payload, camelCase field policy, freshness metadata, requestId and typed error model. - [ ] API exposes the cockpit version boundary and permits only read operations for the cockpit identity. - [ ] UI/demo consumer can load an empty map frame and display success-empty, unauthorized and server-error states. - [ ] Tests cover response serialization, HTTP error categories, service identity enforcement and a request spy proving no business mutation. - [ ] Demo shows the same read-only contract serving a deterministic empty response and a deterministic error response. ## Blocked by None (can start immediately).