fix: normalize imported VS Code theme slugs

[PathGao]

Fixes #187

VS Code theme labels now normalize punctuation runs into one separator before matching the vscodethemes.com URL slug. This makes the documented SynthWave '84 label match the synthwave-84 URL segment.

Depends on #300. Please merge in this order: #286 → #287 → #288 → #293 → #296 → #298 → #300 → this PR.

Validation:

• Reproduced the mismatch against the upstream SynthWave package manifest (SynthWave '84 versus synthwave-84).
• npm run check
• npm test (133 passing)
• cargo test (21 passing)

[PathGao]

@alecdotdev This is the next scoped issue fix in the single chain. It includes a Rust regression test and is based on #300.