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.

internal/handlers/scanner.go

@@ -177,6 +177,38 @@ func (h *Handler) GetScanStatus(c *echo.Context) error {
 	})
 }
 
+// GetActiveScans handles GET /api/scanner/active (admin): every
+// pending/running job. Lets the admin page re-attach to in-flight
+// scans after a page refresh instead of only tracking scans it
+// started itself in this page load.
+func (h *Handler) GetActiveScans(c *echo.Context) error {
+	jobs := h.worker.GetActiveScanJobs()
+	return c.JSON(http.StatusOK, map[string]interface{}{
+		"scanning": len(jobs) > 0,
+		"jobs":     jobs,
+	})
+}
+
+// GetScanSummary handles GET /api/scanner/active-summary (any
+// authenticated user): whether a scan is running and its average
+// progress (0-1). Powers the sitewide sidebar indicator, which must
+// survive page refreshes — websocket events alone only reach pages
+// that were already open when the scan started.
+func (h *Handler) GetScanSummary(c *echo.Context) error {
+	jobs := h.worker.GetActiveScanJobs()
+	progress := 0.0
+	if len(jobs) > 0 {
+		for _, job := range jobs {
+			progress += job.Progress
+		}
+		progress /= float64(len(jobs))
+	}
+	return c.JSON(http.StatusOK, map[string]interface{}{
+		"scanning": len(jobs) > 0,
+		"progress": progress,
+	})
+}
+
 // StartWatchModeForLibrary starts watching a specific library's folders
 func (h *Handler) StartWatchModeForLibrary(ctx context.Context, libraryID pgtype.UUID, adminID pgtype.UUID) error {
 	h.mu.Lock()