refactor: extract model selection logic from delegate-task into focused modules

- Create available-models.ts for model availability checking
- Create model-selection.ts for category-to-model resolution logic
- Update category-resolver, subagent-resolver, and sync modules to import
  from new focused modules instead of monolithic sources

src/tools/delegate-task/sync-continuation.ts

@@ -3,7 +3,9 @@ import type { ExecutorContext, SessionMessage } from "./executor-types"
 import { isPlanFamily } from "./constants"
 import { storeToolMetadata } from "../../features/tool-metadata-store"
 import { getTaskToastManager } from "../../features/task-toast-manager"
-import { getAgentToolRestrictions, getMessageDir, promptSyncWithModelSuggestionRetry } from "../../shared"
+import { getAgentToolRestrictions } from "../../shared/agent-tool-restrictions"
+import { getMessageDir } from "../../shared/session-utils"
+import { promptSyncWithModelSuggestionRetry } from "../../shared/model-suggestion-retry"
 import { findNearestMessageWithFields } from "../../features/hook-message-injector"
 import { formatDuration } from "./time-formatter"