feat(agent): add Gmail workflow affordance

[Hindol Roy Choudhury (Hindolch)]

Summary

Adds a lightweight site affordance layer for BrowserOS workflows, with Gmail compose as the first cached workflow.

This lets agent-facing flows discover higher-level site actions instead of always relying on low-level browser primitives like take_snapshot, click, and fill. The new-tab BrowserOS query path can now recognize email drafting requests and route them into the BrowserOS agent flow instead of treating them as Google searches.

What Changed

• Added site affordance registry and recipe types
• Added affordance tools:
  • site_describe
  • site_intents
  • site_open
  • gmail_compose_draft
• Registered the affordance tools with the server tool registry
• Updated chat mode tool allowlist for affordance discovery
• Added Gmail compose recipe support
• Added new-tab workflow detection for email drafting prompts
• Routed matching new-tab prompts into BrowserOS agent mode
• Added affordance docs

Why

The current browser automation surface is powerful but low-level. For common workflows, the agent has to rediscover the same site capabilities and click paths repeatedly.

This PR adds a first step toward cached browser workflows: the agent can ask what affordances exist for a site/task and call a direct workflow tool when available.

Example:

Recording.2026-05-16.001152.mp4

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