refactor(frontend): type-safe routing and decompose CreateFeedPanel

[gildesmarais]

What changed

• Refactored deriveAppViewModel in frontend/src/appViewModel.ts to accept route: AppRoute directly, eliminating manual string-mapping in the presenter.
• Added getPanelViewState helper in frontend/src/appViewModel.ts to encapsulate calculated view states (isTokenPrompt, isConverting, etc.) outside components.
• Updated useAppPresenter.ts to directly pass route from the router to the view model derivation.
• Decomposed the monolithic CreateFeedPanel in AppPanels.tsx into three focused sub-components (UrlEntrySection, TokenGateSection, and ActionFeedback).
• Updated unit tests in appViewModel.test.ts to cover the routing type changes and the new getPanelViewState helper.

Why

• Locality: Routing and panel presentation logic is no longer scattered or synchronized manually.
• Interface Shrinkage: CreateFeedPanel is now a simple layout orchestrator rather than a complex form parser with dual rendering states.
• Type Safety: Propagating the AppRoute union directly to the view-derivation prevents runtime-mismatches and provides full typescript compiler guarantees.

Risk

• Low. All behaviors and form interactions are preserved, and comprehensive unit tests cover the new structures.

Review map

1. frontend/src/appViewModel.ts — View state derivation and pure getPanelViewState helper mapping.
2. frontend/src/hooks/useAppPresenter.ts — Cleaned up hook wiring passing routes directly.
3. frontend/src/components/AppPanels.tsx — Decomposed UI layout structure.
4. frontend/src/__tests__/appViewModel.test.ts — Validating test coverage.

Validation

• make test-frontend-unit (Exit code: 0)
• make lint-js (Exit code: 0)
• make ready (Exit code: 0)