v1.50.0

• Add the claude:opus-4.8 selection, valid for every role and every command's Claude path: each
  pair agent gains a twin definition (stereo:<role>-opus-4-8) whose frontmatter pins
  claude-opus-4-8 over the same body and tools, because the Agent tool's model parameter accepts
  only the four aliases and claude:opus resolves to the harness's current Opus generation
• Make claude:opus-4.8 the built-in implementer for /stereo:implement and /stereo:quick and
  the tournament's Claude contestant; claude:inherit and the base agents are unchanged
• Correct the routing skill's account of model inheritance to the harness's current resolution
  order: the agent definition decides before CLAUDE_CODE_SUBAGENT_MODEL