theme: Align dark syntax highlighting (#2802)

## Description

Align the macOS Classic Dark, default dark, and website code
highlighting palettes with the terminal-inspired colors.

- Distinguish keywords, methods, types, parameters, strings,
diagnostics, and literals.
- Replace the website's remaining orange/yellow dark accents with the
blue accent, including the logo and illustrations.
- Keep the website theme documentation and Shiki/CSS token mappings in
sync.
- Avoid storing the native resource sampling task on WASM, removing the
`resource_task` dead-code warning without changing native behavior.

## Screenshot

Not included; the changes update theme colors and static website
accents.

## How to Test

- `cargo build --target wasm32-unknown-unknown` from `crates/story-web`
- `cargo test -p gpui-fps`
- `cargo fmt -p gpui-fps --check`
- `bun run build` from `website`
- Parse the modified theme JSON files with `python -m json.tool`
- `git diff --check`

## Checklist

- [x] I have read the [CONTRIBUTING](../CONTRIBUTING.md) document and
followed the guidelines.
- [x] Reviewed the changes in this PR and confirmed AI generated code
(If any) is accurate.
- [ ] Passed `cargo run` for story tests related to the changes.
- [ ] Tested macOS, Windows and Linux platforms performance (if the
change is platform-specific)