fix(web): scan progress — correct percentages, no layout shift, refresh-survivable

Bug: the admin 'Scanning Libraries' widget fed the server's 0-1
progress straight into percent strings and bar widths, so the overall
and per-library percentages capped at '1%' and the bars never filled.
Both now scale by 100 (matching the setup page, which was already
correct).

Bug: scan state only reached clients via websocket events, so a page
opened (or refreshed) mid-scan showed nothing until the next tick —
and the admin widget never re-attached at all. The worker now exposes
active jobs (with their library_id so rows keep their names), served
as GET /api/scanner/active (admin, re-attaches the widget + polling)
and GET /api/scanner/active-summary (any user, restores the sidebar
indicator on load). Idle hides both, exactly as before.

Annoyance: the sidebar's 'Scanning… N%' was a block element between
the logo and the nav, shoving every menu entry down while a scan ran.
The percent now lives inside the fixed-height logo row next to the
spinner (spinner last, so growing digits extend leftward); nothing
below it moves.

templates/header.templ

@@ -24,11 +24,24 @@ templ Header(user User, currentPath string) {
 					@Icon("book-open", "h-6 w-6")
 				</span>
 				<span class="font-bold text-lg tracking-tight" style="color: var(--text-primary)">Bookhoard</span>
+			<!-- Scanning indicator: lives INSIDE the fixed-height logo row so
+			     it can never push the nav entries down. Spinner sits last so
+			     the growing percent extends leftward, not into the spinner. -->
+			<div
+				x-show="scanning"
+				x-cloak
+				x-transition
+				class="ml-auto flex items-center gap-1.5 shrink-0"
+				aria-live="polite"
+			>
+				<span
+					x-show="scanProgress > 0"
+					class="text-xs font-medium"
+					style="color: var(--text-secondary);"
+					x-text="scanProgress + '%'"
+				></span>
 				<svg
-					x-show="scanning"
-					x-cloak
-					x-transition
-					class="h-4 w-4 animate-spin ml-auto"
+					class="h-4 w-4 animate-spin"
 					style="color: var(--accent);"
 					fill="none"
 					viewBox="0 0 24 24"
@@ -36,15 +49,8 @@ templ Header(user User, currentPath string) {
 					<circle class="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" stroke-width="4"></circle>
 					<path class="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z"></path>
 				</svg>
-			</a>
-			<span
-				x-show="scanning && scanProgress > 0"
-				x-cloak
-				x-transition
-				class="block px-5 py-1.5 text-xs font-medium -mt-1"
-				style="color: var(--text-secondary);"
-				x-text="'Scanning… ' + scanProgress + '%'"
-			></span>
+			</div>
+		</a>
 			<!-- Primary navigation -->
 			<nav class="flex-1 px-3 py-4 space-y-0.5 overflow-y-auto">
 				<a href="/dashboard" class={ activeClass(currentPath, "/dashboard") }>