feat(#120): add stealth mode via --stealth flag and AGENT_BROWSER_STEALTH env var

[giulio-leone]

Summary

Adds stealth mode to evade bot detection systems via --stealth CLI flag or AGENT_BROWSER_STEALTH env var.

Changes

• cli/: Add --stealth flag, forward to daemon
• src/browser.ts: Apply evasions via addInitScript() — hide navigator.webdriver, fix chrome.runtime, spoof plugins/languages, patch WebGL+WebGL2 fingerprinting
• Stealth applied to all context creation paths (launch, newWindow, ensurePage, recording)
• Add --disable-blink-features=AutomationControlled launch arg

Usage

agent-browser --stealth open https://example.com
# or
export AGENT_BROWSER_STEALTH=1

Closes #120. Related: #53

[vercel]

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