Migrate docs app to @vercel/geistdocs (#391)

* Migrate docs app to Geistdocs canary

* Fix docs proxy matcher

* Use Geistdocs UI exports

* Update Geistdocs to 1.3.0

* upgrade geistdocs and fix svelte logo

* add copy prompt to certain docs pages

* migrate to 1.5.0

* refactor(docs): use geistdocs v1.5 Badge, CommandPrompt, ThemeAwareImage

Remove the local copies now exported by @vercel/geistdocs@1.5 and import
them from the package instead:

- Badge -> @vercel/geistdocs/components/badge (provider-list)
- CommandPrompt -> @vercel/geistdocs/components/command-prompt (install-command)
- ThemeAwareImage -> @vercel/geistdocs/components/theme-aware-image
  (docs MDX components); migrate the SvelteKit MDX call site to the new
  src={{ light, dark }} API.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(docs): restore install switcher width animation

The hero "For humans / For agents" switcher called router.refresh() on
every toggle (added in #366). That remounts/reconciles the switcher
subtree mid-toggle, resetting the CommandPrompt's measured width state so
the command-line width spring never plays — the line snapped instead of
growing.

Drop the refresh: this flag's only consumer is the switcher itself, so the
optimistic override already shows the correct command and the cookie
persists the choice across reloads (the server reads it and renders the
matching prebuilt `[code]`). The refresh changed nothing visible and only
broke the animation. startTransition() does not help, since router.refresh
already runs as a transition.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* refactor(docs): render home code blocks with geistdocs CodeBlock

Replace the hand-rolled shiki token renderer in HighlightedCode with
fumadocs highlight() + the geistdocs CodeBlock, highlighting with the
shared geistShikiTheme so the home page "Effortless setup" blocks match
the documentation (same syntax colors, header, language icon, copy
button, radius). transformerIcon() fills the filename icon slot; the
caption is preserved below.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(docs): equal-height home code blocks

Grow each HighlightedCode block to fill its grid cell (h-full root +
flex-1 wrapper forcing the Card to h-full) so both columns share the
taller block's height and their captions align. The Card and its <pre>
share bg-background-100, so the shorter block fills seamlessly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* chore(docs): drop dead shadcn tokens (chart-*, sidebar-primary)

Only chart-1..5 and sidebar-primary are unused by both the app and the
geistdocs/fumadocs package CSS. The other shadcn tokens (secondary,
card-foreground, the remaining sidebar-* set, etc.) must stay: the package
stylesheet consumes them via var(--token) for its fd-* utility mappings
and the #nd-sidebar rule, and does not self-define them — the consuming
app has to provide them.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* refactor(docs): migrate consumers off shadcn tokens to Geist scale

Switch every shadcn-token consumer (select, switch, iframe-browser, the
home marketing pages, and the illustrations SVGs) to the Geist --ds-*
scale using the geistdocs PR #75 mapping (foreground->gray-1000,
muted->gray-100, muted-foreground->gray-800, border/input->gray-alpha-400,
ring->gray-600, destructive->red-800, background/card/popover->
background-100, accent->gray-100, etc.).

With no consumers left, drop the entire local shadcn layer from
geistdocs.css (the @theme --color-* mappings and the :root/.dark oklch
palette) and instead override fumadocs --color-fd-* and #nd-sidebar to
--ds-* (so the package's docs UI keeps working without the raw palette),
matching the geistdocs template. The geist utilities themselves come from
@vercel/geistdocs/styles.css.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Update geistdocs.css

* migrate to 1.6.0

* chore(docs): bump @vercel/geistdocs to 1.6.1

Picks up the Next.js logo gradient-id fix so the framework logo renders
correctly in the mobile docs menu.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Update pnpm-lock.yaml

* fix(docs): drop language icons from landing-page code blocks

The home "Effortless setup" snippets are Next.js examples, but the
language-based transformerIcon rendered a React glyph for the .tsx block.
Remove the icons (these blocks never had them) and hide the now-empty
header icon slot so the filename stays flush.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* chore(docs): drop redundant streamdown @source

The streamdown @source pointed at a transitive dep path that doesn't
resolve under pnpm (matched nothing). Streamdown is now sourced upstream
from @vercel/geistdocs's own styles.css, so this line is unneeded.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* update

* bump @vercel/geistdocs

* Update pnpm-lock.yaml

* update

---------

Co-authored-by: christopherkindl <53372002+christopherkindl@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>