refactor(frontend): move S3TT1NGS to its own /settings.html page (#1464 step 2)

Extracts the operator-local preferences (browser-notification toggle)
out of the dashboard tab strip into a standalone /settings.html page,
reached from the H0M3 hub — same minimal-chrome pattern as /flow.html
and /logs.html. The dashboard tab strip is now purely operational.

- new settings.{html,css,js}; settings.js binds NOTIF + renders the
  shared server-warnings banner (matching the other standalone pages).
- drop the S3TT1NGS tab + pane from dashboard.html; the NOTIF.bind()
  toggle wiring moves to settings.js. The dashboard keeps NOTIF.show()
  (approvals / questions) — it reads the same browser permission +
  localStorage mute flag the settings page sets, so firing still works.
- move .notif-row / .btn-notif from dashboard.css to settings.css.
- add a Settings tile to the H0M3 hub; wire the new entries into
  build.mjs and update the nix/frontend.nix asset manifest comment.

First slice of #1464 step 2; the ST4TS page extraction follows separately.

frontend/packages/dashboard/build.mjs

@@ -47,12 +47,12 @@ const staticDir = (p) => resolve(here, 'dist', 'static', p);
 rmSync(dist(''), { recursive: true, force: true });
 mkdirSync(staticDir(''), { recursive: true });
 
-// Bundle all three JS entries. ES-module output, browser target, no minify
+// Bundle the JS entries. ES-module output, browser target, no minify
 // (line-aligned source aids debugging; minification belongs in a later
 // follow-up once asset sizes warrant it). esbuild writes each entry
 // to `static/<name>.js` based on the entryPoint basename.
 await build({
-  entryPoints: [src('tabs.js'), src('flow.js'), src('logs.js'), src('home.js')],
+  entryPoints: [src('tabs.js'), src('flow.js'), src('logs.js'), src('home.js'), src('settings.js')],
   outdir: staticDir(''),
   bundle: true,
   format: 'esm',
@@ -91,7 +91,7 @@ await build({
 // so a swap replaces only it) + theme.css (the semantic derivation
 // layer) + common.css (shared typography, badges, buttons, inbox, side
 // panel) plus its own page-specific bundle.
-for (const entry of ['colors.css', 'theme.css', 'common.css', 'dashboard.css', 'flow.css', 'logs.css', 'home.css']) {
+for (const entry of ['colors.css', 'theme.css', 'common.css', 'dashboard.css', 'flow.css', 'logs.css', 'home.css', 'settings.css']) {
   await build({
     entryPoints: [src(entry)],
     outfile: staticDir(entry),
@@ -101,7 +101,7 @@ for (const entry of ['colors.css', 'theme.css', 'common.css', 'dashboard.css', '
   });
 }
 
-for (const html of ['index.html', 'dashboard.html', 'flow.html', 'logs.html']) {
+for (const html of ['index.html', 'dashboard.html', 'flow.html', 'logs.html', 'settings.html']) {
   copyFileSync(src(html), dist(html));
 }