docs: update BrowserStack mobile config and canonical property names

[MohabMohie]

Motivation

• Clarify BrowserStack native app routing and canonicalize mobile-related property names to match upstream SHAFT_ENGINE changes.
• Ensure documentation shows browserStack.appUrl precedence and uses the canonical authentication keys and platform property for consistent user guidance.

Description

• Add a new “BrowserStack Native Apps” section to docs/Basic_Config/basicConfig2.md that documents browserStack.appUrl precedence and supported remote mobile_app forms (bs://, http://, https://).
• Replace legacy targetPlatform usage with the canonical targetOperatingSystem across mobile/docs examples and snippets, and update CLI examples to -DtargetOperatingSystem.
• Replace legacy BrowserStack credential aliases and remote app examples with the canonical keys browserStack.userName, browserStack.accessKey, and browserStack.appUrl, and update the BrowserStack properties reference to call out these canonical keys and appUrl resolution behavior.
• Files modified include docs/Basic_Config/basicConfig2.md, docs/Getting_Started/Flutter_Testing.mdx, docs/Getting_Started/first_steps_6.md, docs/Getting_Started/integrations.mdx, docs/Getting_Started/setup_mobile.mdx, docs/Getting_Started/shaft_wizard.mdx, docs/Best_Practices/Cross_Platform_Strategy.md, and docs/Properties/PropertiesList.mdx.

Testing

• Ran npm run build (Docusaurus) which completed successfully and generated static files.
• Installed Playwright browsers with npx playwright install chromium and npx playwright install-deps chromium which completed successfully.
• Served the built site with npm run serve and captured a Playwright screenshot of the new BrowserStack section, verifying the content was rendered as expected.

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Codex Task

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