* docs: home page
* updates based on feedback
* respond to review feedback
* docs: update gemini selector strings to "flash-latest"
* Update homepage.css
* Replace google.github.io/adk-docs URLs and /adk-docs/ paths with adk.dev
Migrate all hardcoded documentation references to use the new custom
domain. Update root-relative links to remove the /adk-docs/ subpath
prefix since the site will be served from the root of adk.dev.
* Additional fixes
Joe Fernandez