docs: split text editing guides and add WASM highlighting (#2692)

## Summary

- split the Input, Textarea, and Editor guides for both `gpui-base` and
`gpui-component`, including dedicated native/WASM Base showcase cases
- add a custom `syntect` adapter through `InputHighlighter`, using the
WASM-compatible `fancy-regex` backend for both the Base showcase and the
styled Editor story
- expand the Base Editor source sample and add the live Editor story
after Charts on the homepage
- rename the Base documentation catalog and routes from
`/base/components/*` to `/base/primitives/*` to distinguish unstyled
Base primitives from `gpui-component`
- re-export the custom highlighter interfaces from
`gpui_component::input` and add the website logo to the root README

## Route change

The Base documentation URLs change as follows:

```diff
- /base/components/input
- /base/components/textarea
- /base/components/editor
+ /base/primitives/input
+ /base/primitives/textarea
+ /base/primitives/editor
```

The same `/base/components/<name>` → `/base/primitives/<name>` change
applies to the rest of the Base catalog.

## Test Plan

- `cargo check -p gpui-base --example base_components`
- `cargo check -p gpui-component-story --no-default-features`
- `cargo check -p gpui-component-story`
- `cargo +nightly check --manifest-path
crates/base/examples/wasm/Cargo.toml --target wasm32-unknown-unknown`
- `crates/base/examples/wasm/scripts/build.sh`
- `crates/story-web/scripts/build-wasm.sh`
- `cd website && bun run build`
- `cargo fmt --all`
- `git diff --check`

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Co-authored-by: Codex <codex@openai.com>