fix: fix adk web ui source code serving path

[kalenkevich]

Please ensure you have read the contribution guide before creating a pull request.

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Closes:
• Trying to run ADK Web fails: Cannot GET /dev-ui/ #308
• Devtools UI server fails to server the browser assets return 404 #305

Problem:
CLI entrypoint was bundled and because of that file paths have been broken since the #245.

Solution:
Changed bundled version as entrypoint for ADK CLI to not bundled esm version of that. This ensures that relative path to the browser data will be handled correctly.

Testing Plan

Added integration test to test that ADK WEB is loaded correctly for 2 cases:

• When using adk web ./folder CLI command.
• When using AdkApiServer from @google/adk-devtools

Manual End-to-End (E2E) Tests:

Please provide instructions on how to manually test your changes, including any necessary setup or configuration. Please provide logs or screenshots to help reviewers better understand the fix.

• Ran npm run build in the dev directory to verify that the build completes successfully and the files are placed in the expected directory (./dist/browser).

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas. (Simple cleanup, no comments needed).
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

Add any other context or screenshots about the feature request here.

None.