refactor(cli): split doctor/model-resolution and run/events into focused modules

Doctor checks:
- model-resolution-cache.ts, model-resolution-config.ts
- model-resolution-details.ts, model-resolution-effective-model.ts
- model-resolution-types.ts, model-resolution-variant.ts

Run events:
- event-formatting.ts, event-handlers.ts
- event-state.ts, event-stream-processor.ts

src/cli/doctor/checks/model-resolution-effective-model.ts

@@ -0,0 +1,27 @@
+import type { ModelRequirement } from "../../../shared/model-requirements"
+
+function formatProviderChain(providers: string[]): string {
+  return providers.join(" → ")
+}
+
+export function getEffectiveModel(requirement: ModelRequirement, userOverride?: string): string {
+  if (userOverride) {
+    return userOverride
+  }
+  const firstEntry = requirement.fallbackChain[0]
+  if (!firstEntry) {
+    return "unknown"
+  }
+  return `${firstEntry.providers[0]}/${firstEntry.model}`
+}
+
+export function buildEffectiveResolution(requirement: ModelRequirement, userOverride?: string): string {
+  if (userOverride) {
+    return `User override: ${userOverride}`
+  }
+  const firstEntry = requirement.fallbackChain[0]
+  if (!firstEntry) {
+    return "No fallback chain defined"
+  }
+  return `Provider fallback: ${formatProviderChain(firstEntry.providers)} → ${firstEntry.model}`
+}