Draft changelog: X Activity API and usage updates for Aug 30

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Summary

Adds an Aug 30, 2026 changelog entry covering user-facing product changes shipped since the last entry (Aug 13).

Changes

• New: filter qualifiers (conversation_type, direction) for X Activity API subscriptions
• New: broadcast.start and broadcast.end public events in the X Activity API
• New: GET /2/usage/credits endpoint for PPU credit balance
• Update: is_subscriber field in broadcast.chat event payloads

Context

Sourced from PRs #342, #324, #329, and #340 merged to main since Aug 13. Docs-only fixes (nav additions, page fixes, doc corrections) were excluded.

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Project	Status	Preview	Updated (UTC)
x-corp	🟢 Ready	View Preview	Aug 30, 2026, 11:09 PM

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