backstage release v0.129.1

AI chat: always log network-level diagnostics (request URL, response status / headers, fetch errors, SSE stream lifecycle including premature termination) to the browser console so a “Network error” banner can be triaged from a user report without requiring the ai-chat-verbose-debugging feature flag. Verbose payload-level logging (messages, system prompt, tool schemas, per-event SSE detail) remains gated on the feature flag in non-production builds. See ./docs/releases/v0.129.1-changelog.md for more information.