Draft changelog: streaming latency and user context auth

[mintlify]

Summary

Adds a Sep 9, 2026 changelog entry covering product changes shipped since the last entry (Sep 1).

Changes

• Streaming endpoints P99 latency improved from ~6-7 seconds to ~4-5 seconds
• Webhook management endpoints now accept OAuth 2.0 user context authentication
• Activity API subscription update/delete endpoints now accept OAuth 1.0a and OAuth 2.0 user context

Context

No PRs were merged since the last changelog entry. These changes were identified from the automated OpenAPI spec syncs and related doc updates on main between Sep 2 and Sep 9.

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Project	Status	Preview	Updated
x-corp	🟢 Ready	View Preview	Sep 9, 2026, 2:15 AM

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