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/Common/OverviewToolbar.tsx

@@ -1,5 +1,5 @@
 import { useMutation } from "@tanstack/react-query"
-import { Check, Loader2, Plus, Search, Trash2 } from "lucide-react"
+import { Check, Plus, Search, Trash2 } from "lucide-react"
 import { motion } from "motion/react"
 import { type ReactNode, useRef, useState } from "react"
 
@@ -13,6 +13,7 @@ import {
   DialogTitle,
   DialogTrigger,
 } from "@/components/ui/dialog"
+import { FluksioLoader } from "@/components/ui/fluksio-loader"
 import { Input } from "@/components/ui/input"
 import {
   Tooltip,
@@ -170,7 +171,7 @@ export function OverviewToolbar({
               aria-label="Publish all changes"
               data-testid="publish-all"
             >
-              {publishing ? <Loader2 className="animate-spin" /> : <Check />}
+              {publishing ? <FluksioLoader /> : <Check />}
             </Button>
           </span>
         </TooltipTrigger>