Modernize Babel build tooling and share preset config

[timotheeguerin]

What

Cleans up and modernizes the Babel-based build tooling, removing duplicated configuration and giving the Rollup/Vite plugin a real API.

@alloy-js/babel-preset

• Converted from plain JS to TypeScript with real type declarations, so consumers import the preset without @ts-expect-error.
• package.json hygiene: description/author/homepage/bugs/exports/types, build/clean scripts, node >=22.

@alloy-js/rollup-plugin

• Real typed AlloyPluginOptions (addSourceInfo, sourceMaps) that are actually forwarded (previously ignored).
• Adds a Vite config hook that auto-configures esbuild.jsx: "preserve" and the source resolve/ssr conditions, so consumers no longer set these by hand.
• Typed PluginOption return (was any).

Consumers

• @alloy-js/cli and the plugin compose the typed preset chain inline (@babel/preset-typescript + Alloy preset).
• Removed the now-redundant esbuild/resolve.conditions/ssr boilerplate from 16 vitest.config.ts files.

Validation

• pnpm build ✔
• pnpm test — 243 files / 2103 tests ✔
• pnpm run lint (0 warnings), format:check, sync-publish-config:check, chronus verify ✔

Notes

The stale assumption that onlyRemoveTypeImports: false was required is no longer true — #443 re-enabled the Babel 8 default via explicit type imports, so the preset chain uses typescriptPreset plainly.

[github-actions]

All changed packages have been documented.

• ✅ @alloy-js/babel-preset
• ✅ @alloy-js/cli
• ✅ @alloy-js/core
• ✅ @alloy-js/csharp
• ✅ @alloy-js/go
• ✅ @alloy-js/java
• ✅ @alloy-js/json
• ✅ @alloy-js/markdown
• ✅ @alloy-js/msbuild
• ✅ @alloy-js/python
• ✅ @alloy-js/rollup-plugin
• ✅ @alloy-js/typescript
• ✅ @alloy-js/typespec

Show changes

@alloy-js/babel-preset - feature ✏️

@alloy-js/babel-preset now ships with TypeScript type declarations, so consumers can import the preset without @ts-expect-error.

@alloy-js/rollup-plugin - feature ✏️

The Rollup/Vite plugin now accepts addSourceInfo and sourceMaps options and automatically configures esbuild for Alloy (jsx: "preserve" plus the source resolve conditions). Consumers no longer need to set these by hand in their Vite/Vitest config.

@alloy-js/cli - internal ✏️

Rely on the Rollup/Vite plugin to configure esbuild, removing the duplicated esbuild/resolve boilerplate from each package's vitest.config.ts.

@alloy-js/core - internal ✏️

Rely on the Rollup/Vite plugin to configure esbuild, removing the duplicated esbuild/resolve boilerplate from each package's vitest.config.ts.

@alloy-js/csharp - internal ✏️

Rely on the Rollup/Vite plugin to configure esbuild, removing the duplicated esbuild/resolve boilerplate from each package's vitest.config.ts.

@alloy-js/go - internal ✏️

Rely on the Rollup/Vite plugin to configure esbuild, removing the duplicated esbuild/resolve boilerplate from each package's vitest.config.ts.

@alloy-js/java - internal ✏️

Rely on the Rollup/Vite plugin to configure esbuild, removing the duplicated esbuild/resolve boilerplate from each package's vitest.config.ts.

@alloy-js/json - internal ✏️

Rely on the Rollup/Vite plugin to configure esbuild, removing the duplicated esbuild/resolve boilerplate from each package's vitest.config.ts.

@alloy-js/markdown - internal ✏️

Rely on the Rollup/Vite plugin to configure esbuild, removing the duplicated esbuild/resolve boilerplate from each package's vitest.config.ts.

@alloy-js/msbuild - internal ✏️

Rely on the Rollup/Vite plugin to configure esbuild, removing the duplicated esbuild/resolve boilerplate from each package's vitest.config.ts.

@alloy-js/python - internal ✏️

Rely on the Rollup/Vite plugin to configure esbuild, removing the duplicated esbuild/resolve boilerplate from each package's vitest.config.ts.

@alloy-js/typescript - internal ✏️

Rely on the Rollup/Vite plugin to configure esbuild, removing the duplicated esbuild/resolve boilerplate from each package's vitest.config.ts.

@alloy-js/typespec - internal ✏️

Rely on the Rollup/Vite plugin to configure esbuild, removing the duplicated esbuild/resolve boilerplate from each package's vitest.config.ts.