De-template the frontend and apply the design system

- FastAPI branding replaced throughout: title, favicon, logo (now the org/
  brand SVGs), footer links, route titles; workspace package renamed
- shadcn primitives restyled to the component radius/shadow map: pill
  controls, rounded-lg surfaces, shadow-e1/e2/e3
- floating frosted AppSidebar over a bg-card content region
- theme storage key aligned with the pre-paint script, MotionConfig added
- scripts/capture-screenshots.mjs backs the root 'make verify'

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/main.tsx

@@ -5,6 +5,7 @@ import {
   QueryClientProvider,
 } from "@tanstack/react-query"
 import { createRouter, RouterProvider } from "@tanstack/react-router"
+import { MotionConfig } from "motion/react"
 import { StrictMode } from "react"
 import ReactDOM from "react-dom/client"
 import { ApiError, OpenAPI } from "./client"
@@ -42,11 +43,13 @@ declare module "@tanstack/react-router" {
 
 ReactDOM.createRoot(document.getElementById("root")!).render(
   <StrictMode>
-    <ThemeProvider defaultTheme="dark" storageKey="vite-ui-theme">
-      <QueryClientProvider client={queryClient}>
-        <RouterProvider router={router} />
-        <Toaster richColors closeButton />
-      </QueryClientProvider>
+    <ThemeProvider defaultTheme="system" storageKey="fluksio-ui-theme">
+      <MotionConfig reducedMotion="user">
+        <QueryClientProvider client={queryClient}>
+          <RouterProvider router={router} />
+          <Toaster richColors closeButton />
+        </QueryClientProvider>
+      </MotionConfig>
     </ThemeProvider>
   </StrictMode>,
 )