Adds explicit tier preference to arm selection so the router
deterministically prefers lower-cost arms before falling back:
tier 0: CLI agents (IsCLIAgent=true, subprocess/claude|gemini|vibe)
tier 1: local models (IsLocal=true, ollama/llamacpp)
tier 2: API providers (everything else)
Within a tier, quality/cost scoring still applies. filterFeasible still
gates on quality thresholds, so a low-quality local arm won't beat a
high-quality API arm when the task's minimum threshold rules it out.
Also adds Arm.Disabled: arms with Disabled=true are excluded from
auto-routing but remain selectable via ForceArm.
Implementation: armTier helper + selectBest refactored to try tiers in
order, bestScored picks within a tier. router.Select skips disabled arms
in allArms collection (forced arm bypasses disable check).
vikingowl
6883c2a041