refactor(navigation): factory-style use case + controller

- Use case (get-header) → factory function with IGetHeaderUseCase alias
- Controller renamed header.controller.ts → get-header.controller.ts (verb-noun); converted to factory function with IGetHeaderController alias
- DI module wires factories with .toDynamicValue()
- tRPC router resolves controller via container
- Use case + controller tests refactored to direct factory injection (no container rebinding)
- container.test.ts verifies IGetHeaderUseCase + IGetHeaderController symbols

Refactor log: §1, §4.1, §4.2, §5.1
Spec: §6.4

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

packages/navigation/src/di/symbols.ts

@@ -1,3 +1,7 @@
 export const NAVIGATION_SYMBOLS = {
   IHeaderRepository: Symbol.for("navigation:IHeaderRepository"),
+  // Use cases
+  IGetHeaderUseCase: Symbol.for("navigation:IGetHeaderUseCase"),
+  // Controllers
+  IGetHeaderController: Symbol.for("navigation:IGetHeaderController"),
 } as const;