fix: remove WorkBuddy non-stream chat timeout

[caigee-cmd]

Summary

• Remove the inherited 120-second HTTP client timeout for WorkBuddy non-streaming SSE aggregation; request context still controls cancellation.
• Preserve body read errors instead of masking them as missing [DONE].
• Add regression coverage for long responses, cancellation, truncated bodies, and shared client isolation.
• Freeze existing v0.4.2 notes and add bilingual release notes.

Validation

• go test ./internal/providers/workbuddy -run TestChatNonStreamReadLifecycle -count=5
• go test ./...
• python3 scripts/release-notes.py validate
• git diff --check