refactor(delegate-task): deduplicate DelegatedModelConfig + registry refactor

- Move DelegatedModelConfig to src/shared/model-resolution-types.ts
- Re-export from delegate-task/types.ts (preserving import paths)
- Replace background-agent/types.ts local duplicate with shared import
- Consolidate model-settings-compatibility.ts registry patterns

src/shared/model-resolution-types.ts

@@ -1,5 +1,16 @@
 import type { FallbackEntry } from "./model-requirements"
 
+export interface DelegatedModelConfig {
+  providerID: string
+  modelID: string
+  variant?: string
+  reasoningEffort?: string
+  temperature?: number
+  top_p?: number
+  maxTokens?: number
+  thinking?: { type: "enabled" | "disabled"; budgetTokens?: number }
+}
+
 export type ModelResolutionRequest = {
   intent?: {
     uiSelectedModel?: string