fix(brain): redirect / to /docs/observer/dashboard.html (browser-smoke fix)

Browser smoke (Playwright) revealed that rewriting path internally without
changing the response URL left the browser's base URL as /, breaking
relative <script src="dashboard.js"> and ../automation-graph-data.js
references. 302 redirect makes the browser settle on /docs/observer/,
which resolves the relative paths correctly. All 4 views verified clean
(0 console errors). Screenshots: brain-dashboard-{map,replay,feed,aggregate}-view.png.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tools/brain-dashboard-server.mjs

@@ -50,7 +50,13 @@ export function createServer(root = REPO_ROOT) {
       return;
     }
     let path = url.split('?')[0];
-    if (path === '/') path = '/docs/observer/dashboard.html';
+    if (path === '/') {
+      // Redirect (not rewrite) so the browser's base URL becomes /docs/observer/,
+      // which makes relative <script src="dashboard.js"> and ../automation-graph-data.js resolve correctly.
+      res.writeHead(302, { Location: '/docs/observer/dashboard.html' });
+      res.end();
+      return;
+    }
     const abs = resolveStaticPath(path, root);
     if (!abs || !existsSync(abs) || !statSync(abs).isFile()) {
       res.writeHead(404, { 'Content-Type': 'text/plain; charset=utf-8' });