Use the brand loading mark instead of lucide's spinner

Copies index/frontend's FluksioLoader component and its
`.fluksio-loader-line` rule into the app (the shadcn duplication model, so
the CSS travels with the component) and swaps every Loader2 pending state
over: the router's pending screen, the flow dock's Run and Publish, the
dashboard editor's Publish, the overview toolbar's Publish-all and
LoadingButton. One loading mark across both shells.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K1moruzue2kTJd3uVisgNk

frontend/src/components/Dashboard/DashboardEditor.tsx

@@ -1,14 +1,6 @@
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query"
 import { useNavigate } from "@tanstack/react-router"
-import {
-  Check,
-  ExternalLink,
-  Loader2,
-  Pencil,
-  Plus,
-  Settings2,
-  X,
-} from "lucide-react"
+import { Check, ExternalLink, Pencil, Plus, Settings2, X } from "lucide-react"
 import { motion } from "motion/react"
 import { type CSSProperties, useEffect, useRef, useState } from "react"
 import {
@@ -36,6 +28,7 @@ import {
   DialogHeader,
   DialogTitle,
 } from "@/components/ui/dialog"
+import { FluksioLoader } from "@/components/ui/fluksio-loader"
 import {
   Popover,
   PopoverContent,
@@ -720,7 +713,7 @@ export function DashboardEditor({
                       data-testid="publish-dashboard"
                     >
                       {save.isPending || publish.isPending ? (
-                        <Loader2 className="size-3.5 animate-spin" />
+                        <FluksioLoader className="size-3.5" />
                       ) : (
                         <Check className="size-3.5" />
                       )}