feat(admin): make dashboard live and disk-aware

Wire dashboard panels to real alerts, activity, boxes, and users data instead of static mock rows.

Enable working dashboard actions (close alerts, close low alerts, cleanup expired boxes, exports, and navigation).

Update storage overview to use real filesystem free/total space from the uploads volume.

Make top alert chip data-driven across admin pages.

lib/server/admin_boxes.go

@@ -37,6 +37,7 @@ type adminBoxView struct {
 	CompleteFiles     int                `json:"complete_files"`
 	PendingFiles      int                `json:"pending_files"`
 	FailedFiles       int                `json:"failed_files"`
+	TotalSizeBytes    int64              `json:"total_size_bytes"`
 	TotalSizeLabel    string             `json:"total_size_label"`
 	CreatedAtLabel    string             `json:"created_at_label"`
 	CreatedAtISO      string             `json:"created_at_iso"`
@@ -203,6 +204,7 @@ func (app *App) buildAdminBoxView(boxID string) (adminBoxView, error) {
 	boxView := adminBoxView{
 		ID:                summary.ID,
 		FileCount:         summary.FileCount,
+		TotalSizeBytes:    summary.TotalSize,
 		TotalSizeLabel:    summary.TotalSizeLabel,
 		CreatedAtLabel:    adminTimeLabel(summary.CreatedAt),
 		CreatedAtISO:      formatBrowserTime(summary.CreatedAt),