⚡ refactor: Migrate @librechat/client build to tsdown (#13596)

* ⚡ refactor: Migrate @librechat/client build from Rollup to tsdown

Mirrors the data-schemas migration. Replaces Rollup (rpt2 + postcss) with
tsdown (rolldown + oxc); the package build drops from tens of seconds to ~0.3s.

- Emit isolated-declaration .d.ts via oxc (dts.oxc) and enforce
  isolatedDeclarations in tsconfig for editor DX (source made clean: explicit
  export type annotations added across src, no `any`).
- Extract component CSS to dist/style.css so the CJS output stays valid
  CommonJS (the prior postcss runtime-injection produced an ESM import in the
  CJS bundle that breaks jest/require). Imported once in the client app entry;
  Vite bundles it for the app.
- Repoint package.json to dual .mjs/.cjs + .d.mts/.d.cts and add ./style.css
  and ./package.json exports.
- Update CI build-cache keys to hash tsdown.config.mjs; remove rollup.config.js.

* 🔧 chore: address Codex review on client tsdown migration

- Add tsdown.config.mjs to turbo.json build `inputs` so changes to the new
  bundler config invalidate the Turbo cache (the shared inputs only listed the
  rollup configs). Also covers the already-migrated data-schemas.
- Name the memoized default export (ControlComboboxMemo) instead of the
  codefix-generated `_default_1`, for clearer stack traces / grepping.

.github/workflows/frontend-review.yml

@@ -57,7 +57,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: packages/client/dist
-          key: build-client-package-${{ runner.os }}-${{ hashFiles('packages/client/src/**', 'packages/client/tsconfig*.json', 'packages/client/rollup.config.js', 'packages/client/package.json', 'packages/data-provider/src/**', 'packages/data-provider/tsconfig*.json', 'packages/data-provider/tsdown.config.mjs', 'packages/data-provider/package.json') }}
+          key: build-client-package-${{ runner.os }}-${{ hashFiles('packages/client/src/**', 'packages/client/tsconfig*.json', 'packages/client/tsdown.config.mjs', 'packages/client/package.json', 'packages/data-provider/src/**', 'packages/data-provider/tsconfig*.json', 'packages/data-provider/tsdown.config.mjs', 'packages/data-provider/package.json') }}
 
       - name: Build client-package
         if: steps.cache-client-package.outputs.cache-hit != 'true'

.github/workflows/playwright-mock.yml

@@ -90,7 +90,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: packages/client/dist
-          key: build-client-package-${{ runner.os }}-${{ hashFiles('package-lock.json', 'packages/client/src/**', 'packages/client/tsconfig*.json', 'packages/client/rollup.config.js', 'packages/client/package.json', 'packages/data-provider/src/**', 'packages/data-provider/tsconfig*.json', 'packages/data-provider/tsdown.config.mjs', 'packages/data-provider/package.json') }}
+          key: build-client-package-${{ runner.os }}-${{ hashFiles('package-lock.json', 'packages/client/src/**', 'packages/client/tsconfig*.json', 'packages/client/tsdown.config.mjs', 'packages/client/package.json', 'packages/data-provider/src/**', 'packages/data-provider/tsconfig*.json', 'packages/data-provider/tsdown.config.mjs', 'packages/data-provider/package.json') }}
 
       - name: Build client-package
         if: steps.cache-client-package.outputs.cache-hit != 'true'
@@ -101,7 +101,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: client/dist
-          key: build-client-app-e2e-${{ runner.os }}-${{ hashFiles('package-lock.json', 'client/src/**', 'client/public/**', 'client/scripts/post-build.cjs', 'client/index.html', 'client/package.json', 'client/vite.config.*', 'client/tsconfig*.json', 'client/tailwind.config.*', 'client/postcss.config.*', 'packages/client/src/**', 'packages/client/tsconfig*.json', 'packages/client/rollup.config.js', 'packages/client/package.json', 'packages/data-provider/src/**', 'packages/data-provider/tsconfig*.json', 'packages/data-provider/tsdown.config.mjs', 'packages/data-provider/package.json') }}
+          key: build-client-app-e2e-${{ runner.os }}-${{ hashFiles('package-lock.json', 'client/src/**', 'client/public/**', 'client/scripts/post-build.cjs', 'client/index.html', 'client/package.json', 'client/vite.config.*', 'client/tsconfig*.json', 'client/tailwind.config.*', 'client/postcss.config.*', 'packages/client/src/**', 'packages/client/tsconfig*.json', 'packages/client/tsdown.config.mjs', 'packages/client/package.json', 'packages/data-provider/src/**', 'packages/data-provider/tsconfig*.json', 'packages/data-provider/tsdown.config.mjs', 'packages/data-provider/package.json') }}
 
       - name: Build client app
         if: steps.cache-client-app.outputs.cache-hit != 'true'