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/agent-logger.ts

@@ -59,12 +59,12 @@ export interface AgentLoggerOptions {
  * detailed argument summaries via {@link summarizeToolArgs}.
  *
  * Produces `onText` and `onToolStart` callbacks compatible with
- * `createKbAgent`'s `AgentOptions` interface.
+ * `createFnAgent`'s `AgentOptions` interface.
  *
  * @example
  * ```ts
  * const logger = new AgentLogger({ store, taskId, onAgentText, onAgentTool });
- * const { session } = await createKbAgent({
+ * const { session } = await createFnAgent({
  *   cwd: worktreePath,
  *   onText: logger.onText,
  *   onToolStart: logger.onToolStart,