feat(web): book-detail annotations banner — ?loc= reader jumps, single/zip markdown export

Objective 7 (web half). The 'Annotations' button slides a right-hand
banner (annotations_banner.templ + annotations-banner.ts) fed by the
existing per-book GET endpoints: friendly labels (Section N parsed from
the CFI spine / Page N from the PDF envelope / NN% + first-words
fallbacks), capped highlight previews, rich x-html expansion through the
objective-6 markdown pipeline, and per-row 'Open reader here' jumps
riding /readers/:uuid?loc= (consumeLocJump: jump outranks stored
progress for that open; URL stripped before sync can echo it). WEB-ONLY
export: single .md or one-file-per-item zip via fflate — item format
identical both modes ('# friendly label' / '# selection text' headers,
raw markdown bodies, no raw CFIs anywhere).

Verified live in Brave: 12 restored highlights + a markdown note
labeled/expanded correctly; the jump navigated, landed on the right
chapter and consumed ?loc=; export produced the 13-item .md (friendly
headers only) and a valid 13-entry zip. Book-detail's existing
recently-deleted modal stays untouched (banner is additive).

templates/book_detail.templ

@@ -107,6 +107,13 @@ templ BookDetail(user User, book handlers.MediaDetail, errorMessage string) {
 										<span class="badge ml-1" style="background-color: var(--accent-muted); color: var(--accent);">{ book.NotesCount + book.HighlightsCount }</span>
 									}
 								</button>
+								<button @click="toggleAnnotationsBanner()" class="btn btn-secondary px-5 py-2.5">
+									@Icon("bookmark", "h-4 w-4")
+									<span>Annotations</span>
+									if book.NotesCount + book.HighlightsCount > 0 {
+										<span class="badge ml-1" style="background-color: var(--accent-muted); color: var(--accent);">{ book.NotesCount + book.HighlightsCount }</span>
+									}
+								</button>
 							if user.Role == "admin" {
 								<button @click="showMetadataEditor()" class="btn btn-secondary px-5 py-2.5">
 									@Icon("edit", "h-4 w-4")
@@ -434,6 +441,7 @@ templ BookDetail(user User, book handlers.MediaDetail, errorMessage string) {
 			</div>
 			@ProgressSyncModal(user, book)
 			@NotesHighlightsModal(user, book)
+			@AnnotationsBanner(book)
 			if user.Role == "admin" {
 				@MetadataEditorModal(book)
 			}