feat: suivi de la progression de lecture par livre

- API : nouvelle table book_reading_progress (migration 0016) et module
  reading_progress.rs avec GET/PATCH /books/:id/progress (token read)
- API : GET /books/:id enrichi avec reading_status, reading_current_page,
  reading_last_read_at via LEFT JOIN
- Backoffice : badge de statut (Non lu / En cours · p.N / Lu) sur la page
  de détail et overlay sur les BookCards
- OpenSpec : change reading-progress avec proposal/design/specs/tasks

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

apps/api/src/main.rs

@@ -7,6 +7,7 @@ mod libraries;
 mod api_middleware;
 mod openapi;
 mod pages;
+mod reading_progress;
 mod search;
 mod settings;
 mod state;
@@ -106,6 +107,7 @@ async fn main() -> anyhow::Result<()> {
         .route("/books/:id", get(books::get_book))
         .route("/books/:id/thumbnail", get(books::get_thumbnail))
         .route("/books/:id/pages/:n", get(pages::get_page))
+        .route("/books/:id/progress", get(reading_progress::get_reading_progress).patch(reading_progress::update_reading_progress))
         .route("/libraries/:library_id/series", get(books::list_series))
         .route("/search", get(search::search_books))
         .route_layer(middleware::from_fn_with_state(state.clone(), api_middleware::read_rate_limit))