refactor(core): split index.ts and config-handler.ts into focused modules

Main entry point:
- create-hooks.ts, create-tools.ts, create-managers.ts
- plugin-interface.ts: plugin interface types
- plugin/ directory: plugin lifecycle modules

Config handler:
- agent-config-handler.ts, command-config-handler.ts
- tool-config-handler.ts, mcp-config-handler.ts
- provider-config-handler.ts, category-config-resolver.ts
- agent-priority-order.ts, prometheus-agent-config-builder.ts
- plugin-components-loader.ts

src/plugin-handlers/category-config-resolver.ts

@@ -0,0 +1,9 @@
+import type { CategoryConfig } from "../config/schema";
+import { DEFAULT_CATEGORIES } from "../tools/delegate-task/constants";
+
+export function resolveCategoryConfig(
+  categoryName: string,
+  userCategories?: Record<string, CategoryConfig>,
+): CategoryConfig | undefined {
+  return userCategories?.[categoryName] ?? DEFAULT_CATEGORIES[categoryName];
+}