refactor(ui): sharpen buttons + inputs to rounded (4px) for modern minimal SaaS look

V2 sharper radii system aligned with Stripe Dashboard / Linear / Vercel
aesthetic — the v1 rounded-lg (8px) on buttons still felt too soft.

New scale:
- Buttons (CTA, submit, ghost, secondary): rounded-lg → rounded (4px)
- Form inputs (text/email/password/select/textarea): rounded-md → rounded (4px)
- Checkboxes: rounded-sm (2px) added explicitly to consent + remember-me
- Cards (pricing, bento, content panels): rounded-xl → rounded-lg (8px)
- Small icon tiles (w-10 h-10 / w-12 h-12 grad-bg squares): rounded-md → rounded
- Pills, badges, avatars, status orbs: rounded-full (KEPT)
- Inline code in legal CSS: rounded (4px) (KEPT)
- Legal blockquote/pre/draft-callout border-radius: 8px → 4px

Files modified (24):
- templates/macros/{button,bento,pricing_card}.html
- templates/marketing/{landing,tarifs,fonctionnalites,conformite,contact}.html
- templates/auth/{check_email,forgot_password,magic_link_request,
  oauth_finish_signup,passkey_setup,reset_password,totp_setup,totp_verify,
  verify_success}.html
- templates/billing/{success,cancel}.html
- templates/legal/{_layout,index}.html
- templates/{register,login}.html
- tests/test_marketing_landing_template.py (assertions updated to match v2)

Verification:
- 18/18 legal page tests pass (tests/_run_legal_pages_windows.py)
- 58/58 marketing landing tests pass

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

templates/billing/cancel.html

@@ -24,7 +24,7 @@
   <div class="max-w-[820px] mx-auto px-6">
     <h2 id="info-title" class="sr-only">Que faire ensuite</h2>
 
-    <div class="bg-white p-8 rounded-xl border border-brand-border mb-8">
+    <div class="bg-white p-8 rounded-lg border border-brand-border mb-8">
       <h3 class="text-lg font-bold mb-3 text-brand-navy">Pourquoi avoir hésité&nbsp;?</h3>
       <p class="text-sm text-brand-navy/80 leading-relaxed mb-4">
         Si vous avez une question sur les forfaits, la conformité Loi&nbsp;25 ou la mise en service, notre équipe peut vous accompagner sans pression commerciale.