fix(cli): address Gemini test report — local mode, validate bug, offline flag

A. acr init --local: new local mode, no Cloudflare account required;
   config defaults to mode:local when ~/.arcrun/config.yaml missing

B. validate node-count bug: removed faulty input/output node heuristic
   that dropped start/end nodes from config check; now all nodes except
   reserved 'input' keyword must have config entries

C. acr validate --offline: skip remote component-existence and credentials
   checks; local mode also auto-skips these checks

D. parts.ts: replace require('node:fs') with static import (ES module fix)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cli/src/commands/parts.ts

@@ -3,7 +3,7 @@
  * acr parts scaffold <component> — 輸出 config 範本
  * acr parts publish <component>  — 提交零件至公眾 registry
  */
-import { readFileSync, existsSync } from 'node:fs';
+import { readFileSync, existsSync, readdirSync } from 'node:fs';
 import { join } from 'node:path';
 import chalk from 'chalk';
 import ora from 'ora';
@@ -226,7 +226,6 @@ function loadLocalComponents(): ComponentInfo[] {
   for (const dir of dirs) {
     if (existsSync(dir)) {
       const components: ComponentInfo[] = [];
-      const { readdirSync } = require('node:fs');
       for (const name of readdirSync(dir)) {
         const contractPath = join(dir, name, 'component.contract.yaml');
         if (existsSync(contractPath)) {