fix(core): restore bundler resolution for source-imported deps - #41885

What

Restore a green typecheck on v2 by reverting the three NodeNext compiler options added to packages/core/tsconfig.json in 4acdeff (refactor(core): require explicit import extensions), while keeping that commit's ~300 files of explicit .js import extensions.

Before / After

Before: bun typecheck failed repo-wide at v2 HEAD (c217ebe2ad), blocking the pre-push hook for everyone. packages/core imports @opencode-ai/ai and @ff-labs/fff-bun as raw TypeScript sources (their package exports point at src/*.ts), so their files are compiled inside core's program under core's compiler options. With moduleResolution: NodeNext, their extensionless relative imports produce hundreds of TS2835 errors, which cascade into packages/plugin and packages/desktop as TS2305 "has no exported member" failures for Message, SystemPart, CommandInfo, ConnectionInfo, and others.

After: Core resolves modules with the bundler settings from @tsconfig/bun again. The explicit .js extensions in core sources remain valid (TypeScript maps ./agent.js to agent.ts in bundler resolution too), so none of the 300-file refactor is reverted. All 33 packages typecheck.

How

• packages/core/tsconfig.json: remove "module": "NodeNext", "moduleResolution": "NodeNext", and "allowImportingTsExtensions": false.
• packages/core/script/migration.ts: emit .js extensions from the renderMigration, renderSchema, and renderRegistry templates. 4acdeff hand-updated the generated schema.gen.ts, migration.gen.ts, and migration files but not the generator, so the database-migration freshness check regenerated old-style imports and failed CI (Current database schema is stale). The templates now reproduce the checked-in files byte for byte.

Scope

• This does not add tooling to enforce explicit extensions, which was presumably the intent of the flags. Strict NodeNext is not currently feasible while the repo consumes raw-TS dependencies: @ff-labs/fff-bun ships extensionless .ts sources in node_modules, which cannot be edited. Enforcement would need a lint rule (e.g. ESLint import/extensions or a Biome rule) instead of compiler options, or built .d.ts boundaries for source-imported packages. Happy to follow up either way — flagging for @thdxr since 4acdeff landed directly on v2.

Testing

• bun typecheck at repo root: 33/33 packages pass (previously @opencode-ai/desktop and core itself failed)
• bun typecheck in packages/core including tsconfig.tests.json
• bun script/migration.ts --check in packages/core passes with no changes to generated files (fails on v2 HEAD and on the first commit of this branch)