Add trackEmbedded config option for cross-origin iframe cookie support

[alazarchuk]

Summary

• Adds trackEmbedded boolean config option (default: false) to enable session tracking in cross-origin iframe contexts
• When true, cookies are written with SameSite=None; Secure attributes, which browsers require for cross-origin cookie access
• Adds Playwright tests verifying cookie attributes are present/absent based on the config value

Test plan

• trackEmbedded=false (default): verify no SameSite=None or Secure attributes on cookie assignments
• trackEmbedded=true: verify all cookie assignments include both SameSite=None and Secure
• All 29 existing tests continue to pass

🤖 Generated with Claude Code

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