`.tsx` widgets break `frontmcp build` typecheck without `jsx` flag and React types

[alexmercerpo]

Describe the bug
After adding a .tsx widget under src/, frontmcp build fails with TypeScript errors even though the widget is bundled separately at runtime by uipack/esbuild (with React externalized). The default tsconfig.json has include: ["src/**/*"] and no jsx option, so the build-time typecheck step compiles the widget .tsx against a config that has no JSX support and no react types. Errors:

src/tools/ui-card.widget.tsx(1,26): error TS2307: Cannot find module 'react' or its corresponding type declarations.
src/tools/ui-card.widget.tsx(42,5): error TS17004: Cannot use JSX unless the '--jsx' flag is provided.
src/tools/ui-card.widget.tsx(42,5): error TS7026: JSX element implicitly has type 'any' ...

To Reproduce
Steps to reproduce the behavior:

1. Create a FrontMCP v1.3.0 project with the default tsconfig.json.
2. Add a .tsx widget file under src/ (e.g. src/tools/ui-card.widget.tsx).
3. Run yarn build (frontmcp build).
4. See TS2307, TS17004, TS7026 errors against the widget file.

Expected behavior
Either (a) the scaffold/generator adds "jsx": "react-jsx" and react devDeps automatically when a UI tool with a FileSource widget is created, (b) frontmcp build excludes widget files (e.g. *.widget.tsx) from the server typecheck (since they are compiled separately by uipack/esbuild at render time), or (c) a skill clearly documents the requirement.

Fix that worked: add "jsx": "react-jsx" to tsconfig.json and yarn add -D react react-dom @types/react @types/react-dom (dev-only; externalized at runtime, so they do not bloat the server bundle — confirmed ~8 KB bundle).

Screenshots
N/A.

Desktop (please complete the following information):

• OS: macOS (Darwin 25.3.0)
• Browser: N/A
• Version: @frontmcp/sdk@1.3.0, @frontmcp/uipack@1.3.0; TypeScript 5.x; Node 22+

Smartphone (please complete the following information):

• N/A

Additional context
Related: #443, #444 (FileSource resolution), and #454 (CDN-based React widgets don't render in Claude).