fix(chatgpt): pin browser targets for reproducible bundles

[ScriptedAlchemy]

The embedded ChatGPT app changed according to browser configuration outside the checkout. A developer-directory .browserslistrc targeting Chrome 51 / Safari 10 was inherited locally, while CI used Rsbuild 2's default targets. That changed both CSS lowering and JavaScript output and caused the byte-for-byte freshness failure in #3219.

Pin the extension's browser targets to the existing Rsbuild 2 defaults (Chrome/Edge 107, Firefox 104, Safari 16), and regenerate the self-contained app through the maintained build script. The generated app is byte-identical to the independent Linux regeneration in #3200; the server bundle is unchanged. The external browser configuration remains untouched.

Verification through the Bazel-managed Node runtime:

• Real negative check: removing only the target pin makes the canonical app fail check:embedded with the ancestor configuration present.
• Restoring the pin passes the full embedded app/server freshness check, including CI=true.
• The regenerated app matches fix(runtime): repair cross-host storage and verification journeys #3200's Linux bytes (477886 bytes; SHA-256 8fb719178d012702fe07f1f3894e45b02bb218f89c51857533bb72ca90e2e9b7).
• Commitlint and diff checks pass.

Fixes #3219. This completes the cause investigation behind #3200's generated-file refresh and prevents a developer's ancestor configuration from reintroducing it.

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[devin-ai-integration]

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