feat(ui): add Rescan button to Edit Metadata dialog

Adds a Rescan button to the MetadataEditorModal footer that POSTs to the
new per-book rescan endpoint, with rescanning state (disabled + spinner,
matching the existing Mark Read pattern), success/error toasts, and a
page reload to pick up the refreshed cover and metadata.

web/src/book-detail.ts

@@ -97,6 +97,7 @@ interface MetadataEditorState {
   coverFile: Blob | null;
   coverAction: string;
   saving: boolean;
+  rescanning: boolean;
   userRating: number;
   ratingHover: number;
   ratingSaving: boolean;
@@ -110,6 +111,7 @@ interface MetadataEditorState {
   generateCover(): Promise<void>;
   removeCover(): void;
   saveMetadata(): Promise<void>;
+  rescanBook(): Promise<void>;
   starFill(i: number): string;
   ratingText(): string;
   setRating(value: number): Promise<void>;
@@ -149,6 +151,7 @@ Alpine.data("bookDetail", () => {
     coverFile: null as Blob | null,
     coverAction: "keep",
     saving: false,
+    rescanning: false,
     userRating: 0,
     ratingHover: 0,
     ratingSaving: false,
@@ -559,6 +562,31 @@ Alpine.data("bookDetail", () => {
       }
     },
 
+    async rescanBook() {
+      if (this.rescanning) return;
+      this.rescanning = true;
+      const mediaId = getMediaId();
+      try {
+        const resp = await fetch(`/api/media-items/${mediaId}/rescan`, {
+          method: "POST",
+          headers: { Authorization: getAuthHeader() },
+        });
+        if (!resp.ok) {
+          const err = await resp.json().catch(() => ({}));
+          throw new Error(err.error || "Failed to rescan book");
+        }
+        showToast("Book rescanned successfully", "success");
+        setTimeout(() => window.location.reload(), 500);
+      } catch (e) {
+        showToast(
+          e instanceof Error ? e.message : "Failed to rescan book",
+          "error",
+        );
+      } finally {
+        this.rescanning = false;
+      }
+    },
+
     async searchEditorTags() {
       const libraryId = document.body.getAttribute("data-library-id") || "";
       if (!this.tagSearch || this.tagSearch.length < 2 || !libraryId) {