feat(ms-ai-architect): sitemap-based KB change detection system

Adds a zero-dependency Node.js pipeline that polls Microsoft Learn sitemaps
weekly to detect when source documentation changes. Replaces the broken
mtime-based staleness check (all files had identical mtime after release).

Components:
- build-registry.mjs: extracts 1342 URLs from 387 reference files
- poll-sitemaps.mjs: streams ~18 child sitemaps, matches against registry
- report-changes.mjs: prioritized change report (critical/high/medium/low)
- discover-new-urls.mjs: finds relevant new MS Learn pages not yet covered
- run-weekly-update.mjs: orchestrator with --force/--discover/--dry-run

Integration:
- session-start hook reads change-report.json instead of broken mtime check
- hook triggers background poll if >7 days since last check
- generate-skills --update reads change report for targeted MCP updates

Current stats: 69% match rate (924/1342 URLs tracked via sitemaps).
~31% unmatched due to Microsoft URL restructuring (ai-foundry/openai paths).

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

plugins/ms-ai-architect/scripts/kb-update/run-weekly-update.mjs

@@ -0,0 +1,70 @@
+#!/usr/bin/env node
+// run-weekly-update.mjs — Orchestrator for weekly KB update pipeline.
+// Runs: poll → report → (optional) discover, sequentially.
+// Usage: node run-weekly-update.mjs [--force] [--discover] [--dry-run]
+
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { execFileSync } from 'node:child_process';
+import { loadRegistry } from './lib/registry-io.mjs';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const DATA_DIR = join(__dirname, 'data');
+
+const force = process.argv.includes('--force');
+const discover = process.argv.includes('--discover');
+const dryRun = process.argv.includes('--dry-run');
+
+const DAY_MS = 24 * 60 * 60 * 1000;
+
+function run(script, args = []) {
+  const fullPath = join(__dirname, script);
+  console.log(`\n--- Running ${script} ${args.join(' ')} ---`);
+  try {
+    execFileSync('node', [fullPath, ...args], {
+      stdio: 'inherit',
+      timeout: 10 * 60 * 1000, // 10 min max per step
+    });
+  } catch (err) {
+    console.error(`${script} failed: ${err.message}`);
+    process.exit(1);
+  }
+}
+
+// --- Main ---
+const registry = loadRegistry(DATA_DIR);
+const lastPoll = registry.last_poll ? new Date(registry.last_poll) : null;
+const daysSince = lastPoll ? (Date.now() - lastPoll.getTime()) / DAY_MS : Infinity;
+
+if (!force && daysSince < 7) {
+  console.log(`Last poll: ${Math.floor(daysSince)} day(s) ago. Next in ${Math.ceil(7 - daysSince)} day(s).`);
+  console.log('Use --force to run anyway.');
+  process.exit(0);
+}
+
+if (dryRun) {
+  console.log('DRY RUN — would execute:');
+  console.log('  1. poll-sitemaps.mjs' + (force ? ' --force' : ''));
+  console.log('  2. report-changes.mjs');
+  if (discover) console.log('  3. discover-new-urls.mjs');
+  process.exit(0);
+}
+
+// Ensure registry exists
+if (Object.keys(registry.urls).length === 0) {
+  console.log('Registry empty — building from reference files first...');
+  run('build-registry.mjs');
+}
+
+// Step 1: Poll sitemaps
+run('poll-sitemaps.mjs', force ? ['--force'] : []);
+
+// Step 2: Generate change report
+run('report-changes.mjs');
+
+// Step 3: Optional discovery
+if (discover) {
+  run('discover-new-urls.mjs', ['--limit', '500']);
+}
+
+console.log('\n=== Weekly update complete ===');