Rook v1.5.6

What's Changed

• [codex] Add video poster sidecar producer by @bringfire in #145
• [codex] Add video frame sidecar producer by @bringfire in #146
• Add bounded video sidecar startup backfill by @bringfire in #147
• [codex] Bundle LGPL FFmpeg for video sidecars by @bringfire in #148
• [codex] Add durable media gallery import by @bringfire in #149
• [codex] tighten gh_edit partial failure contract by @bringfire in #150
• [codex] Guard GH legacy routes with readiness boundary by @bringfire in #151
• Panel-locked Rhino targeting for Rook MCP by @bringfire in #152
• [codex] harden hosted panel lifecycle by @bringfire in #153

Full Changelog: v1.5.5...v1.5.6