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/tools.ts

@@ -1,7 +1,7 @@
 import { tool, type ToolDefinition } from "@opencode-ai/plugin"
 import type { DelegateTaskArgs, ToolContextWithMetadata, DelegateTaskToolOptions } from "./types"
 import { DEFAULT_CATEGORIES, CATEGORY_DESCRIPTIONS } from "./constants"
-import { log } from "../../shared"
+import { log } from "../../shared/logger"
 import { buildSystemContent } from "./prompt-builder"
 import type {
   AvailableCategory,