RunnerModels map in models.go grows unbounded

[msoedov]

internal/models/models.go:42-89 has a hardcoded RunnerModels map with 35 model entries across 5 runners (claude_code, gemini, codex, copilot, opencode). Every new model or runner requires editing this map.

Used by IsValidModelForRunner() for CLI validation and scheduler.go for runtime checks.

Proposal:

• Load model lists from config or embed file rather than hardcoding
• Alternatively, make each runner own its model list so additions are scoped to the runner package