feat: syntax-highlight blog post code blocks at SSR

[vivek7405]

Closes #897

Blog code fences rendered monochrome. This highlights them at SSR (zero client JS) by reusing the canonical tokenizer in website/lib/highlight.ts, the same token classes the home page and @webjsdev/ui docs use, so colors match across every WebJs surface.

What changed

• website/lib/highlight.ts: new highlightToHtml(code) string emitter (reuses the existing tokenize() + CLASS map; HTML-escapes token text).
• website/modules/blog/utils/render-post.ts: JS/TS fences render highlighted spans; sh/plain fences stay escaped text.
• Token color CSS (.t-*, light + dark) promoted from the inline app/page.ts block to global public/input.css so the blog route inherits it. Home page still loads the same palette from the global sheet.

Test plan

• Unit: highlightToHtml spans + escaping of <, &, backticks
• Unit: render-post ts fence highlights, sh fence stays plain
• Visual: /blog/ code blocks colored; home page unchanged
• Self-review loop clean

Draft while I add tests and self-review.

[vivek7405]

Review: bare-fence highlighting bug, fixed

First self-review round caught a real one. The highlighted-language set included '' (empty language), so a bare ```` fence got run through the JS tokenizer. Blog posts use bare fences for command output (the-naming-saga has npm error text; the new JS-concepts post has a serializer probe-output block), and JS-tokenizing that mis-colors words like `Forbidden` and `403`.

Fixed in 1cc566a: bare and unknown-language fences stay plain escaped text; only ts/tsx/js/jsx/javascript/typescript highlight, matched case-insensitively. Added tests pinning a bare fence to plain output (the counterfactual that would have caught this) and a case-insensitive lang. Verified live: the-naming-saga now renders 0 token spans, the JS-concepts post keeps its ts fences colored but leaves the probe-output block plain.

[vivek7405]

Review: second round clean

Rendered all 42 blog posts through the renderer: zero tokenizer errors. The language gate holds. Across the corpus there are 144 bare fences and 14 sh plus a few json/jsonc/html fences that all stay plain, and 94 ts / 5 js / 1 tsx fences that highlight. Nothing else to fix.