v0.4.0-alpha.9

What's Changed

• feat(extension): add Browser Control Plane Phase A by @whshang in #69
• docs: add executable GA release gate (G1-G25) by @whshang in #70
• docs(ga-gate): G10 controlled rollback UAT evidence by @whshang in #72
• docs(g20): native install path + command-contract hygiene by @whshang in #71
• docs(ga-gate): mark G20 PARTIAL after #71 install-path fix by @whshang in #75
• feat(cli): top-level install/rollback/uninstall user path (G3) by @whshang in #74
• feat(doctor): product layer ownership map (G8) by @whshang in #73
• docs(ga): refresh gate after #73/#74 by @whshang in #77
• chore(release): prepare Rust alpha.9 by @whshang in #76

Full Changelog: v0.4.0-alpha.8...v0.4.0-alpha.9