fix(opencode): skip typechecking generated models snapshot

[kitlangton]

Summary

• generate the models snapshot as models-snapshot.js plus a tiny models-snapshot.d.ts instead of a giant models-snapshot.ts as const
• add // @ts-nocheck to the generated JS payload so TypeScript treats the snapshot as opaque data
• keep runtime behavior the same while avoiding a large typecheck cliff after running the build script

Benchmarks

• with a generated models-snapshot.ts as const on origin/dev: tsc --noEmit --extendedDiagnostics took about 89s, tsgo --noEmit --incremental false --extendedDiagnostics took about 3.57s
• with this patch and a generated models-snapshot.js + models-snapshot.d.ts: tsc --noEmit --extendedDiagnostics took about 23s, tsgo --noEmit --incremental false --extendedDiagnostics took about 2.42s
• a clean checkout without generated snapshot artifacts is already fast; this fixes the slowdown that appears after the snapshot is generated locally