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/admin_templ.go

@@ -29,7 +29,7 @@ func Admin(user User, stats AdminStats) templ.Component {
 			templ_7745c5c3_Var1 = templ.NopComponent
 		}
 		ctx = templ.ClearChildren(ctx)
-		templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 1, "<!doctype html><html lang=\"en\"><head><meta charset=\"UTF-8\"><meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\"><title>Admin Dashboard - Bookhoard</title><link href=\"/static/style.css\" rel=\"stylesheet\"><link rel=\"icon\" type=\"image/svg+xml\" href=\"/static/favicon.svg\"></head><body x-data=\"admin\" x-init=\"loadWatchStatus()\" class=\"theme-{ user.Theme }\">")
+		templ_7745c5c3_Err = templruntime.WriteString(templ_7745c5c3_Buffer, 1, "<!doctype html><html lang=\"en\"><head><meta charset=\"UTF-8\"><meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\"><title>Admin Dashboard - Bookhoard</title><link href=\"/static/style.css\" rel=\"stylesheet\"><link rel=\"icon\" type=\"image/svg+xml\" href=\"/static/favicon.svg\"></head><body x-data=\"admin\" x-init=\"loadWatchStatus(); checkActiveScans()\" class=\"theme-{ user.Theme }\">")
 		if templ_7745c5c3_Err != nil {
 			return templ_7745c5c3_Err
 		}