v0.7.26

Note: auto-release was skipped because the squash-merge subject chore: bump version to 0.7.26 (#628) no longer matched the strict $ anchor in auto-release.yml. Cutting manually; regex fix follow-up incoming.

What ships

• bench --tier {smoke,speed,harness,all} (#621)
• bench --tier ... --submit unified flow (#623)
• doctor slimmed to pure env-health (#622)
• community-benchmarks schema v2 (#620)
• qwen3-0.6b-4bit alias (#624)