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/Flow/FlowDock.tsx

@@ -2,7 +2,6 @@ import { useReactFlow } from "@xyflow/react"
 import {
   AlertCircle,
   Check,
-  Loader2,
   Maximize2,
   Pause,
   Pencil,
@@ -18,6 +17,7 @@ import { useEffect, useState } from "react"
 
 import type { ValidationIssue } from "@/client"
 import { Button } from "@/components/ui/button"
+import { FluksioLoader } from "@/components/ui/fluksio-loader"
 import { Separator } from "@/components/ui/separator"
 import {
   Tooltip,
@@ -273,7 +273,7 @@ export function FlowDock({
                 data-testid="run-flow"
               >
                 {running ? (
-                  <Loader2 className="size-4 animate-spin" />
+                  <FluksioLoader className="size-4" />
                 ) : (
                   <Play className="size-4" />
                 )}
@@ -348,7 +348,7 @@ export function FlowDock({
                 {!connected ? (
                   <WifiOff className="size-3.5" />
                 ) : saving || publishing ? (
-                  <Loader2 className="size-3.5 animate-spin" />
+                  <FluksioLoader className="size-3.5" />
                 ) : (
                   <Check className="size-3.5" />
                 )}