feat: plakat redesign for subpages (projects, books, legal, privacy)

- Shared SubpageShell (HeaderClient paper strip + ink footer) and SubpageIntro,
  btn/ghost/card helpers in app/_ui/subpage.tsx
- Projects list: poster cards with hard ink shadows, filter pills, ink search field;
  no fake 800ms skeleton and no framer-motion opacity:0 in SSR
- Project detail: poster hero, .plakat-prose markdown, links/stack aside,
  back link works without JS
- Books: server-side fetch (visible without JS), cover + rating pills
- Legal notice / privacy: moved to app/_ui/*Client.tsx, root routes removed
  (middleware always redirects to /[locale]), consent reset via useConsent
- ProjectThumbnail rebuilt on Plakat tokens
- Old Header.tsx + test removed; brown/cream/sand palettes and unused
  glass-panel/admin-glass(-light)/liquid-bg-blob/float CSS dropped
  (liquid palette, glass-card, admin-glass-card stay for admin + 404)
- .plakat-prose replaces the missing typography plugin

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/CHANGING_TEXTS.md

@@ -105,8 +105,8 @@ The privacy policy and legal notice use a **dynamic CMS system**:
 
 ### Option 2: Edit Static Fallback
 If you haven't set up CMS content, the fallback static content is in:
-- Privacy Policy: `/app/privacy-policy/page.tsx` (lines 76-302)
-- Legal Notice: `/app/legal-notice/page.tsx`
+- Privacy Policy: `/app/_ui/PrivacyPolicyClient.tsx` (Fallback-Text, sonst CMS-Seite `privacy-policy`)
+- Legal Notice: `/app/_ui/LegalNoticeClient.tsx` (Fallback-Text, sonst CMS-Seite `legal-notice`)
 
 ⚠️ **Note**: Static content is hardcoded in German. For CMS-based content, you can manage both languages separately.