refactor(design): single source of truth — wevisto-design.css

v2 tokens were duplicated: in design-v2.scss for the SPA, inlined in
login.html.twig for Twig. Two places to keep in sync.

Now: one shared /public/css/wevisto-design.css loaded by every Twig
standalone template AND linked from the SPA index.html. It contains:
- Brand constants (yellow / navy / fonts)
- v2 tokens with per-theme dusk overrides
- v2 base body bg + editorial typography defaults
- v2 overrides for the .card / .btn / .field-error / .logo-badge
  patterns used across all Twig templates

The SPA's design-v2.scss now holds only SPA-specific composition:
side rail at desktop, frame card, theme swatch harbor preview,
settings polish. No token duplication.

Result: changing a v2 color in one file flows to every surface in both
worlds. Adding v2 to another Twig template only requires the existing
shared CSS link (already wired up to all 11 standalone templates).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

templates/help/index.html.twig

@@ -7,6 +7,7 @@
     <link rel="icon" type="image/png" sizes="32x32" href="/build/icons/favicon-32.png?v=20260515-vviewfinder">
     <link rel="icon" type="image/png" sizes="16x16" href="/build/icons/favicon-16.png?v=20260515-vviewfinder">
     <link rel="apple-touch-icon" sizes="180x180" href="/build/icons/apple-touch-icon.png?v=20260515-vviewfinder">
+    <link rel="stylesheet" href="/css/wevisto-design.css">
     <title>Setup help — WeVisto</title>
     <style>
         *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }