Online-first MAUI data layer + post/note browsing

[fboucher]

Parent PRD

#110

Depends on

#120 (MAUI project + auth), #122 (local SQLite layer)

Summary

Implement the IOfflineDataService / OfflineDataService (online path only at this stage). Wire the SharedUI components into the MAUI shell so the app is fully demoable while online: browse posts, view post detail, create/edit notes, view summaries.

Data layer

interface IOfflineDataService
{
    Task<List<Post>> GetPostsAsync();
    Task<Post?> GetPostAsync(string id);
    Task SaveNoteAsync(Note note);
    Task UpdateNoteAsync(Note note);
    Task MarkPostReadAsync(string id);
    // ... mirrors UI needs
}

OfflineDataService (online path): calls remote API via PostNoteClient, mirrors results to ILocalDataService.

UI wiring

Connect SharedUI components (from #119) to IOfflineDataService:

• Post list page
• Post detail page
• Note dialog (create/edit)
• Summary list
• Settings

Acceptance Criteria

• IOfflineDataService and OfflineDataService created
• Online path: reads and writes go to the API and mirror to local SQLite
• Post list, post detail, note creation, summary list visible and functional in the MAUI app while online
• App uses Bearer token from SecureStorage for all API calls

Stories from PRD

User stories 2, 3, 4, 14, 15