docs(release): align 0.2 capability messaging

[lucasli1015]

Summary

• remove Marketplace from the top-level v0.2 README and GitHub release narrative used by hosted users
• document the verified Auto / 256K / 1M provider context settings from feat(runtime): add model context and session thinking controls #454, including 900K compaction, 64K recent-token retention, and model/provider limits
• preserve the detailed technical plugin changelog for local and self-hosted users
• add the context-window guidance to the bilingual provider docs

Validation

• npm run docs:check
• npm run docs:build
• git diff --check

After merge, the mutable GitHub Release v0.2.0 and v0.2.2 bodies will be updated from the corrected release-note files.

Closes #539

[HaoxuanLiTHUAI]

Reviewed the release narrative against the shipped 0.2.2 contracts and Cloud availability. The top-level Marketplace claim is removed, the 1M context description matches #454 (900K compaction / 64K retention), model/provider limits are explicit, and the detailed local/self-hosted plugin changelog remains intact. Docs checks and required CI are green.