Unify branding: VT323 logotype across website, TUI, and OAuth pages

- Add VT323 ASCII art logo to logo.mjs as single source of truth
- Website nav and hero use VT323 font via AsciiLogo.astro component
- TUI header and CLI help render the ASCII logo with block-centered alignment
- OAuth callback pages (Pi and alphaXiv) show branded feynman logotype
- Auto-set recommended model after provider login

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

website/src/components/AsciiLogo.astro

@@ -7,13 +7,13 @@ interface Props {
 const { class: className = '', size = 'hero' } = Astro.props;
 
 const sizeClasses = size === 'nav'
-  ? 'text-lg'
-  : 'text-4xl sm:text-5xl md:text-6xl';
+  ? 'text-2xl'
+  : 'text-6xl sm:text-7xl md:text-8xl';
 ---
 
 <span
   class:list={[
-    "font-['Silkscreen'] text-accent font-bold tracking-tight inline-block",
+    "font-['VT323'] text-accent inline-block tracking-tighter",
     sizeClasses,
     className,
   ]}

website/src/layouts/Base.astro

@@ -22,7 +22,7 @@ const { title, description = 'Research-first AI agent', active = 'home' } = Astr
   <title>{title}</title>
   <link rel="preconnect" href="https://fonts.googleapis.com" />
   <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
-  <link href="https://fonts.googleapis.com/css2?family=Silkscreen:wght@400;700&display=swap" rel="stylesheet" />
+  <link href="https://fonts.googleapis.com/css2?family=VT323&display=swap" rel="stylesheet" />
   <ViewTransitions fallback="none" />
   <script is:inline>
     (function() {

website/src/pages/index.astro

@@ -1,10 +1,12 @@
 ---
 import Base from '../layouts/Base.astro';
+import AsciiLogo from '../components/AsciiLogo.astro';
 ---
 
 <Base title="Feynman — The open source AI research agent" active="home">
   <section class="text-center pt-24 pb-20 px-6">
     <div class="max-w-2xl mx-auto">
+      <AsciiLogo size="hero" class="mb-4" />
       <h1 class="text-5xl sm:text-6xl font-bold tracking-tight mb-6" style="text-wrap: balance">The open source AI research agent</h1>
       <p class="text-lg text-text-muted mb-10 leading-relaxed" style="text-wrap: pretty">Investigate topics, write papers, run experiments, review research, audit codebases &mdash; every output cited and source-grounded</p>
       <div class="inline-flex items-center gap-3 bg-surface rounded-lg px-5 py-3 mb-8 font-mono text-sm">