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/components/PageContextMenu.svelte

@@ -4,6 +4,7 @@
     import Tag from '@lucide/svelte/icons/tag';
     import Download from '@lucide/svelte/icons/download';
     import Link2 from '@lucide/svelte/icons/link-2';
+    import Sparkles from '@lucide/svelte/icons/sparkles';
 
     /**
      * Floating context menu anchored at `(anchor.x, anchor.y)` in
@@ -25,7 +26,10 @@
         onSaveImage,
         onCopyLink,
         collectionsCount,
-        tags
+        tags,
+        canAnalyze = false,
+        onAnalyzePage,
+        analyzeState = 'idle'
     }: {
         open: boolean;
         anchor: { x: number; y: number };
@@ -41,6 +45,12 @@
         collectionsCount: number | null;
         /** May be empty. */
         tags: string[];
+        /** Admin-only: show the "Queue for analysis" action. */
+        canAnalyze?: boolean;
+        /** Force-enqueue the current page for AI analysis. */
+        onAnalyzePage?: () => void;
+        /** Transient state for the analyze action's label. */
+        analyzeState?: 'idle' | 'busy' | 'done' | 'error';
     } = $props();
 
     let menuEl: HTMLDivElement | undefined = $state();
@@ -170,6 +180,24 @@
             <Link2 size={14} aria-hidden="true" />
             <span>Copy page link</span>
         </button>
+        {#if canAnalyze}
+            <div class="divider" aria-hidden="true"></div>
+            <button
+                type="button"
+                class="item"
+                onclick={onAnalyzePage}
+                disabled={analyzeState === 'busy'}
+                data-testid="page-context-analyze"
+            >
+                <Sparkles size={14} aria-hidden="true" />
+                <span>
+                    {#if analyzeState === 'busy'}Queueing…
+                    {:else if analyzeState === 'done'}Queued for analysis ✓
+                    {:else if analyzeState === 'error'}Queue failed — retry
+                    {:else}Queue for analysis{/if}
+                </span>
+            </button>
+        {/if}
         <div class="divider" aria-hidden="true"></div>
         <p class="hint" data-testid="page-context-collections-line">
             {collectionsLine}