v0.1.19 — per-model concurrency budgets

Added

• Per-model concurrency budgets. All three consilium advisors independently flagged head-of-line blocking: one global p-limit meant a burst of background small-model calls occupied the whole FIFO queue ahead of interactive fusion turns. Every real upstream model now gets its own gate in front of the global limiter (resilience.limiterFor(model)), with strict model-gate → global-slot acquisition order (uniform ordering — no lock cycle; confirmed deadlock-free in a pre-tag adversarial review). A saturated model holds at most its budget of global-queue positions. Config: upstream.per_model_concurrency (map, keyed by real upstream model name) and upstream.per_model_concurrency_default; both unset = behavior identical to the previous single global limiter. The shipped fusion.yaml caps deepseek-v4-pro (the Claude Code background-call carrier) at 2. All strategy fallbacks wire the same budgets via resilienceForUpstream, and /v1/models capability discovery is keyed too.