add header rescan button to apply officer-items changes without restart

New POST /api/rescan re-runs the boot item setup (ensureItemDirs +
ensureToolLoader) and returns live item counts; the header button calls it
and invalidates the item query caches so the UI refetches from disk.

Also fix ensure-tool-loader to write into OFFICER_ITEMS_DIR/extensions (the
runtime read path) instead of the now-unread DATA_PATH/extensions.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/servers/ensure-tool-loader.ts

@@ -1,11 +1,11 @@
 import { mkdirSync, readFileSync, writeFileSync } from 'node:fs';
 import { join, resolve } from 'node:path';
-import { DATA_PATH } from './data-path';
+import { itemsDir } from './data-path';
 
 const SOURCE_PATH = resolve(import.meta.dir, 'tool-loader-source.ts');
 
 export function ensureToolLoader(): void {
-  const targetDir = join(DATA_PATH, 'extensions', 'tool-loader');
+  const targetDir = join(itemsDir('extensions'), 'tool-loader');
   const targetFile = join(targetDir, 'index.ts');
 
   mkdirSync(targetDir, { recursive: true });