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/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() {