UI redesign step 1/N: Tailwind foundation + Stitch theme + Login + Wizard

Foundation
- Pull in Tailwind via CDN with the full Stitch design tokens
  (palette, typography, spacing, radius) inline in <head>. Preflight
  disabled so the rest of the legacy inline CSS keeps applying until
  each screen is migrated.
- Add Hanken Grotesk + JetBrains Mono + Material Symbols Outlined
  via Google Fonts.
- Replace the page header with the Stitch dark-slate top bar: brand
  on the left, segmented tab nav in the middle, user pill + logout
  on the right. Floating userBadge removed; renderUserBadge() now
  writes the display name into #headerUserName and wires the
  existing logout button.

Login
- Single card mirroring the Stitch login mockup with icon-prefixed
  inputs (person/lock), focus ring, error banner and a primary CTA
  that includes the login glyph. Setup mode swaps the heading,
  shows the orange info bar with admin_panel_settings glyph and
  changes the button to "Administrator anlegen".

Wizard (Schaltung erfassen)
- Step 1: anbieter button grid in Stitch style — bordered cards
  with a material icon, hover lift and primary-coloured outline.
- Step 2: white card with a "← Anbieter ändern" pill in the
  header, two-column layout (Aktivierungsdaten / Vertragsdaten),
  label-caps form labels, JetBrains-Mono numeric inputs for
  dates/ID/phone and a dashed file-drop zone. Save button gains
  the save glyph.

Other screens (Übersicht, Provisionen, Gelöschte, Administration,
Benutzer) still render in the legacy style — those migrations
follow in the next steps.

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

public/login.js

@@ -1,22 +1,29 @@
-// Login page logic. Detects whether initial setup is required and adjusts the form.
+// Login page logic: detects first-run setup mode and swaps the form into
+// admin-creation mode. Talks to /api/auth/setup or /api/auth/login.
 
 (async function init() {
     const errorBox = document.getElementById('errorBox');
+    const errorText = document.getElementById('errorText');
     const setupNote = document.getElementById('setupNote');
+    const setupTopBar = document.getElementById('setupTopBar');
+    const brandIcon = document.getElementById('brandIcon');
     const title = document.getElementById('title');
+    const subtitle = document.getElementById('subtitle');
     const submitBtn = document.getElementById('submitBtn');
+    const submitLabel = document.getElementById('submitLabel');
+    const submitIcon = document.getElementById('submitIcon');
     const form = document.getElementById('loginForm');
     const passwordInput = document.getElementById('password');
 
     let setupMode = false;
 
     function showError(msg) {
-        errorBox.textContent = msg;
-        errorBox.classList.add('visible');
+        errorText.textContent = msg;
+        errorBox.style.display = 'flex';
     }
     function clearError() {
-        errorBox.textContent = '';
-        errorBox.classList.remove('visible');
+        errorText.textContent = '';
+        errorBox.style.display = 'none';
     }
 
     try {
@@ -25,14 +32,21 @@
             const data = await r.json();
             setupMode = !!data.setupRequired;
         }
-    } catch (e) {
-        // Fall through: stay in login mode
+    } catch (_) {
+        // network error -> stay in login mode
     }
 
     if (setupMode) {
         title.textContent = 'Ersteinrichtung';
-        setupNote.style.display = 'block';
-        submitBtn.textContent = 'Administrator anlegen';
+        subtitle.textContent = 'Willkommen beim Provisions-Tracker.';
+        setupNote.style.display = 'flex';
+        setupTopBar.style.display = 'block';
+        submitLabel.textContent = 'Administrator anlegen';
+        submitIcon.textContent = 'person_add';
+        // Brand icon switches to admin look in setup mode
+        brandIcon.classList.remove('bg-primary', 'text-on-primary');
+        brandIcon.classList.add('bg-surface-variant', 'text-on-surface');
+        brandIcon.querySelector('span').textContent = 'admin_panel_settings';
         passwordInput.setAttribute('autocomplete', 'new-password');
         passwordInput.setAttribute('minlength', '8');
     }