docs: update navigation examples to use navigate instead of act

[danieldaquino]

This PR updates some examples that used the previously act call for navigation, to use navigate instead.

More context: #7

Testing

stagehand-rust: ff6eab6
Browser: Browserbase
Steps:

1. Run cargo run --example basic
2. Check the logs and the session recording in Browserbase, ensuring it navigates to the desired page

Result: PASS, the example script successfully navigates to the correct page

[shrey150]

Tested locally - compiles clean and navigation now works correctly (prints success). The step 7 agent error is pre-existing on main. LGTM!