docs: update changelog for v2.2.4

Author: james-6-23

CHANGELOG.md

@@ -1,5 +1,22 @@
 # Changelog
 
+## v2.2.4 - 2026-05-28
+
+### Features
+
+- **Scheduler warm-tier bypass (#176).** Added a scheduler option to skip warm-tier demotion so selected accounts can stay in the healthy scheduling lane.
+- **API Reference image previews.** The Try it panel now renders image responses directly when `/v1/images/generations` or `/v1/images/edits` returns `b64_json`, image URLs, or Responses-style image output, while still keeping the raw JSON visible.
+- **Long-context billing details (#178).** Usage cost tooltips now expose when long-context pricing is active (`input_tokens > 272,000`) and show the actual input, output, and cache-read unit prices used for the request.
+- **Root changelog.** Moved the project changelog to the repository root so release notes and documentation links point to a stable location.
+
+### Fixes
+
+- **WebSocket response continuity (#182).** Fixed WS mode context loss so `previous_response_id` continuation remains connected across `/v1/responses` WebSocket turns.
+- **First-token timeout retries (#172).** First-token timeouts now retry by account-pool round and clear transient unavailable markers after the pool has been tried, reducing false "no available account" failures for small pools.
+- **Banned-account test recovery.** Successful account tests now recover stale banned/error state instead of leaving the account marked unhealthy after the probe succeeds.
+- **Bounded batch account tests.** Batch account tests now keep their execution bounded so duplicate or repeated test requests do not destabilize account state handling.
+- **Version popover clipping.** The version popover is rendered through a portal so sidebar overflow no longer clips the latest-version panel.
+
 ## v2.2.3 - 2026-05-27
 
 ### Features