feat: author pages with /authors/:id route (0.16.0)

- `GET /v1/authors/:id` returns `AuthorWithCount` (id, name, manga_count).
- `GET /v1/authors/:id/mangas` paged works by that author.
- `GET /v1/authors?search=` autocomplete (already used by Phase 1 forms;
  now formally exposed).
- New `/authors/:id` page on the frontend; author chips on the manga
  detail page (added in Phase 1) now link to a real page.
- Extracts `lib/components/MangaCard.svelte` — already used by the home
  page, ready for the collection page in Phase 3.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/api/authors.rs

@@ -0,0 +1,80 @@
+use axum::extract::{Path, Query, State};
+use axum::routing::get;
+use axum::{Json, Router};
+use serde::Deserialize;
+use uuid::Uuid;
+
+use crate::api::pagination::PagedResponse;
+use crate::app::AppState;
+use crate::domain::author::{Author, AuthorWithCount};
+use crate::domain::manga::Manga;
+use crate::error::AppResult;
+use crate::repo;
+
+pub fn routes() -> Router<AppState> {
+    Router::new()
+        .route("/authors", get(list))
+        .route("/authors/:id", get(get_one))
+        .route("/authors/:id/mangas", get(list_mangas))
+}
+
+#[derive(Debug, Deserialize)]
+pub struct ListParams {
+    #[serde(default)]
+    pub search: Option<String>,
+    #[serde(default = "default_limit")]
+    pub limit: i64,
+    #[serde(default)]
+    pub offset: i64,
+}
+
+fn default_limit() -> i64 {
+    10
+}
+
+#[derive(Debug, Deserialize)]
+pub struct MangaListParams {
+    #[serde(default = "default_manga_limit")]
+    pub limit: i64,
+    #[serde(default)]
+    pub offset: i64,
+}
+
+fn default_manga_limit() -> i64 {
+    50
+}
+
+async fn list(
+    State(state): State<AppState>,
+    Query(params): Query<ListParams>,
+) -> AppResult<Json<Vec<Author>>> {
+    let limit = params.limit.clamp(1, 50);
+    let offset = params.offset.max(0);
+    let search = params.search.as_deref().and_then(|s| {
+        let t = s.trim();
+        if t.is_empty() { None } else { Some(t) }
+    });
+    Ok(Json(repo::author::list(&state.db, search, limit, offset).await?))
+}
+
+async fn get_one(
+    State(state): State<AppState>,
+    Path(id): Path<Uuid>,
+) -> AppResult<Json<AuthorWithCount>> {
+    Ok(Json(repo::author::find_with_count(&state.db, id).await?))
+}
+
+async fn list_mangas(
+    State(state): State<AppState>,
+    Path(id): Path<Uuid>,
+    Query(params): Query<MangaListParams>,
+) -> AppResult<Json<PagedResponse<Manga>>> {
+    let limit = params.limit.clamp(1, 200);
+    let offset = params.offset.max(0);
+    // Intentionally does NOT 404 on unknown id — the join naturally
+    // returns zero rows, and the page envelope already conveys that.
+    // Saves a round-trip and matches the shape of GET /mangas.
+    let (items, total) =
+        repo::author::list_mangas_for_author(&state.db, id, limit, offset).await?;
+    Ok(Json(PagedResponse::with_total(items, limit, offset, total)))
+}