Draft changelog: streaming latency and webhook OAuth updates

[mintlify]

Summary

Adds changelog entries for the product changes shipped since the Sep 1 entry.

Changes

• Sep 6: OAuth 2.0 user context is now a supported auth method on the webhook management endpoints and X Activity subscription update/delete endpoints.
• Sep 2: high-volume streaming P99 latency improved from ~6-7 seconds to ~4-5 seconds (including Filtered Stream).

Context

Sourced from changes merged to main since the last changelog entry: the streaming latency update and OpenAPI spec updates adding OAuth 2.0 user-context auth. No merged PRs in the window; scope-order and docs-only edits were excluded.

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Project	Status	Preview	Updated
x-corp	🟢 Ready	View Preview	Sep 6, 2026, 11:09 PM

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