fix(web): banner highlight delete; retention wording states the days

The book-detail banner's highlight rows gain Delete (tombstoned
server-side, restorable from the Deleted modal — same as the reader
drawers already offered). The deleted-annotations modal now says the
retention in plain language — 'kept for 30 days' from the
annotation_tombstone_ttl_days tunable (threaded through BookDetail →
NotesHighlightsModal; 1-day singular and retention-disabled variants
handled) — instead of referencing a settings name a reader cannot see.

templates/book_detail_modals.templ

@@ -128,7 +128,7 @@ templ ProgressSyncModal(user User, book handlers.MediaDetail) {
 	</div>
 }
 
-templ NotesHighlightsModal(user User, book handlers.MediaDetail) {
+templ NotesHighlightsModal(user User, book handlers.MediaDetail, tombstoneDays int) {
 	<div
 		id="notes-modal"
 		class="hidden fixed inset-0 z-50 flex items-center justify-center overflow-y-auto p-4"
@@ -183,7 +183,13 @@ templ NotesHighlightsModal(user User, book handlers.MediaDetail) {
 						<span class="badge" style="background-color: var(--accent-muted); color: var(--accent);">{ len(book.DeletedAnnotations) }</span>
 					</div>
 					<p class="text-xs mb-4" style="color: var(--text-secondary);">
-						Deleted entries are kept for the sync retention window before being removed automatically. Restore returns them to every synced device; Delete permanently removes them immediately.
+						if tombstoneDays == 1 {
+							Deleted entries are kept for 1 day before being removed automatically. Restore returns them to every synced device; Delete permanently removes them immediately.
+						} else if tombstoneDays > 1 {
+							Deleted entries are kept for { tombstoneDays } days before being removed automatically. Restore returns them to every synced device; Delete permanently removes them immediately.
+						} else {
+							Deleted entries are kept until manually purged (retention disabled). Restore returns them to every synced device; Delete permanently removes them immediately.
+						}
 					</p>
 					<div class="space-y-3">
 						for _, ann := range book.DeletedAnnotations {