feat(analysis): admin UI — reader context-menu action + dashboard section

Surfaces the scoped re-enqueue and per-page force-analyze in the UI:

- api/admin: reenqueueAnalysis({onlyUnanalyzed, mangaId, chapterId}) and
  analyzePage(pageId).
- Reader PageContextMenu gains an admin-only "Queue for analysis" item
  (canAnalyze/onAnalyzePage/analyzeState props) wired to the force-analyze
  endpoint with inline busy/done/error feedback; reset per page.
- New /admin/analysis dashboard section + nav tab: scope selector
  (whole library / one manga / one chapter), id input, and an
  "include already-analyzed" toggle (default off), with busy/notice/error.

Tests: vitest for the two clients; Playwright for the context-menu action
(admin vs non-admin) and the admin section (scope + include toggle +
validation). svelte-check + build clean; 262 vitest, 10 new e2e green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/lib/api/admin.ts

@@ -403,3 +403,41 @@ export async function listMissingCovers(
         init
     );
 }
+
+// ---- AI content analysis ---------------------------------------------------
+
+/** Options for the scoped analysis re-enqueue. `mangaId` and `chapterId`
+ *  are mutually exclusive; omit both to target the whole library. */
+export type ReenqueueAnalysisOptions = {
+    /** Skip pages that already have a completed analysis (default true).
+     *  When false, in-scope pages are force re-analyzed. */
+    onlyUnanalyzed?: boolean;
+    mangaId?: string;
+    chapterId?: string;
+};
+
+/** Bulk-enqueue `analyze_page` jobs for all / a manga's / a chapter's
+ *  pages. Returns how many jobs were enqueued. Requires ANALYSIS_ENABLED
+ *  on the backend (503 otherwise). */
+export async function reenqueueAnalysis(
+    opts: ReenqueueAnalysisOptions = {}
+): Promise<{ enqueued: number }> {
+    const body: Record<string, unknown> = {
+        only_unanalyzed: opts.onlyUnanalyzed ?? true
+    };
+    if (opts.mangaId) body.manga_id = opts.mangaId;
+    if (opts.chapterId) body.chapter_id = opts.chapterId;
+    return request<{ enqueued: number }>('/v1/admin/analysis/reenqueue', {
+        method: 'POST',
+        headers: { 'content-type': 'application/json' },
+        body: JSON.stringify(body)
+    });
+}
+
+/** Force re-analysis of a single page (used by the reader context menu). */
+export async function analyzePage(pageId: string): Promise<{ enqueued: boolean }> {
+    return request<{ enqueued: boolean }>(
+        `/v1/admin/pages/${encodeURIComponent(pageId)}/analyze`,
+        { method: 'POST' }
+    );
+}