refactor(FN-2161): standardize on createFnAgent naming

- Rename engine export and call sites to use createFnAgent consistently across runtime flows
- Update core lazy engine loader and dashboard agent-generation/planning/chat paths to reference createFnAgent
- Refresh affected unit and integration tests, including renaming pi-create-kb-agent.test.ts to pi-create-fn-agent.test.ts
- Update AGENTS.md documentation references to match the new createFnAgent name

packages/engine/src/skill-resolver.ts

@@ -6,7 +6,7 @@
  * 2. Optional caller-requested skill names (for per-task overrides)
  *
  * The resolver reads project settings files directly (read-only) and produces
- * a filter set used by createKbAgent's DefaultResourceLoader.skillsOverride.
+ * a filter set used by createFnAgent's DefaultResourceLoader.skillsOverride.
  */
 
 import { existsSync, readFileSync } from "node:fs";