v0.5.4

release: bump version to 0.5.4 and update changelogs

Patch release for inline chart references in summaries:
- {{chart:<id>}} markers let the model embed a previously-generated
  interactive chart into its text summary (rendered in place with type
  switching / fullscreen / export), instead of leaking raw ![...] text
- stabilize inline chart segments during streaming by reusing chart-ref
  chunk references so the reference-keyed <For> no longer disposes +
  re-inits echarts on every token

latest.json is intentionally left untouched; the Release workflow's
update-website-config job regenerates it from update.json + build
signatures after the tag is pushed.