TS7 native compiler (tsc-go) adoption tracking

[krisarmstrong]

Tracking issue for adopting the TypeScript 7 native compiler (`tsc-go` / `@typescript/native-preview`) in stem's UI.

Cross-repo doc

Full plan + benchmarks: MustardSeedNetworks/seed#1066 (`docs/TS7_NATIVE_PREP.md`).

stem-specific measurement

```
tsc (JS, current): 2.58s
tsgo (native): 0.76s
speedup: 3.4×
```

Error output identical (both clean on stem main).

Adoption gates

• Phase 1: Wait for `@typescript/native-preview` `rc` or `next` dist-tag → add as dev dep + `typecheck:fast` script
• Phase 2: TS 7.0 GA → swap `typescript` to 7.0, drop preview package
• Phase 3: After one stable release cycle → switch CI Type-check step to native binary (~1.8s saved per PR)

Risks specific to stem

• The C dataplane has its own build chain unaffected
• Biome 2.4.15 stack-overflow precedent: a similar upstream regression on the native compiler would block CI. Pin exactly when adopting, not with caret

See also

• seed: docs(prep): TypeScript 7 native compiler adoption plan (Wave 5 / #32) seed#1066 (TS7 adoption tracking + doc)
• niac: equivalent tracking issue