Fix broken link to run_app_with_gemini_key.md in examples READMEs

[omarfarouk228]

Description

Fixes #783
The file was moved to docs/usage/ but the links in two example READMEs still pointed to the old path, causing a 404.

Fixed in:

• examples/travel_app/README.md
• examples/simple_chat/README.md

Pre-launch Checklist

• I read the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.
• I read the Contributors Guide.
• I have added sample code updates to the changelog.
• I updated/added relevant documentation (doc comments with ///).

If you need help, consider asking for advice on the #hackers-devrel channel on Discord.

[gemini-code-assist]

Code Review

This pull request fixes broken links to the run_app_with_gemini_key.md documentation in the simple_chat and travel_app example READMEs and updates the genui package changelog. I have no feedback to provide.

_{Note: Security Review has been skipped due to the limited scope of the PR.}

[polina-c]

Thank you for suggestion.

Can you please, fix the conflicts?

[omarfarouk228]

I fixed the conflicts @polina-c

[github-actions]

Package publishing

If you have publishing permissions, you can use the links below to publish the changes after merging this PR.

Package	Version	Status	Publish tag (post-merge)
package:a2ui_core	0.0.1-wip002	ready to publish	a2ui_core-v0.0.1-wip002
package:genai_primitives	0.2.4	ready to publish	genai_primitives-v0.2.4
package:genui	0.9.2	(error) pubspec version (0.9.2) and changelog (0.10.0) don't agree
package:genui_a2a	0.9.0	(error) pubspec version (0.9.0) and changelog (0.10.0) don't agree
package:json_schema_builder	0.1.5	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[polina-c]

It seems the broken links were already fixed previously. But thank you for noticing and submitting the fix. Highly appreciate it.

[jacobsimionato]

Yes, thanks! I'm going to close this now.