REV-37: Specify stable team identity across async work

[warp-agent-staging]

Summary

• Add the product contract for one immutable team identity per logical operation.
• Add the technical design for sealed TeamContext construction, request-edge extraction, scoped spawn helpers, and Agent Mode owner snapshots.
• Split implementation into foundation, Agent Mode/CLI, billing, catalog/policy, and scope-audit stages.
• Map all twelve confirmed investigation risks to those stages.

Review focus

• The recommended defaults for billing scope, workspace-global AI policy, and new-window-only team switching are marked as assumptions pending requester confirmation.
• This PR contains specs only. It has no production code changes.

Jira: https://warp-dev-staging.atlassian.net/browse/REV-37
Origin: https://warpdev.slack.com/archives/C0BREN45G2D/p1787170237056799

Validation

• Checked Markdown whitespace and balanced code fences.
• Verified that only specs/REV-37/PRODUCT.md and specs/REV-37/TECH.md changed.

[warp-agent-staging]

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