fix: enable React Compiler for @lifi/widget and @lifi/wallet-management

[smrnjeet222]

Which Linear task is linked to this PR?

N/A - outside contributor

Why was it implemented this way?

Enables the React Compiler (babel-plugin-react-compiler@^1.0.0, target 19) across the widget toolchain. The widget already runs on React 19, this PR turns on the compiler's automatic memoization.

Wiring

• Library packages (@lifi/widget, @lifi/wallet-management) : added @rolldown/plugin-babel + @babel/core and registered babel-plugin-react-compiler in their tsdown.config.ts so the compiler runs at publish build time. Consumers receive pre-compiled output and don't need to add the plugin themselves.
• App packages (widget-embedded, widget-playground-vite) : registered the plugin via @vitejs/plugin-react's babel.plugins option so the playground / iframe host benefit too.
• knip.json : ignore babel-plugin-react-compiler (only referenced as a string by Babel, not imported).

Picked the tsdown + @rolldown/plugin-babel route over swc/oxc because the React Compiler currently ships only as a Babel plugin, running it through Babel during the rolldown build is the supported path and keeps the rest of the pipeline (rolldown/oxc) untouched.

Codebase implications (no refactor in this PR)

• The compiler auto-memoizes components and hook return values. Going forward, new code should skip manual useMemo / useCallback / React.memo / forwardRef unless there's a measured reason, the compiler handles it.
• Existing usages are intentionally not refactored in this PR to keep the diff reviewable and bisectable. can clean them up incrementally (or via a dedicated codemod PR) once validated the compiler.
• forwardRef is also unnecessary on React 19 (ref is a regular prop), same "don't add new ones, clean up later" rule.

Visual showcase (Screenshots or Videos)

N/A - build-time change, no runtime/UI behavior change.

Checklist before requesting a review

• I have performed a self-review and testing of my code.
• This pull request is focused and addresses a single problem.
• If this PR modifies the Widget API or adds new features that require documentation, I have updated the documentation in the public-docs repository.

[changeset-bot]

🦋 Changeset detected

Latest commit: c21414c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
@lifi/widget	Minor
@lifi/wallet-management	Minor
nft-checkout	Patch
tanstack-router-example	Patch
vite-iframe	Patch

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