feat: Complete UX cleanup - Agent colors & streamlined navigation

Agent Color System:
- Added unique colors for each agent (orchestrator: purple, researcher: teal, negotiator: red, ar_manager: yellow)
- CSS variables and utility classes (.agent-*, .agent-badge-*, .agent-border-*)
- Tasks table now shows colored left border per agent
- Agent names displayed in their brand color

Navigation Simplification:
- Removed 'Email Log' from main menu (reduced clutter)
- Email Log now accessible via link in Emails page
- Active state for both /emails and /email-log on Emails nav item

Visual Improvements:
- Agent assignments now visually distinct at a glance
- Cleaner, more focused navigation menu
- Better information architecture

templates/emails.html

@@ -104,6 +104,22 @@
     </div>
   </div>
 </div>
+
+<div class="row g-4 mt-4">
+  <div class="col-12">
+    <div class="card">
+      <div class="card-header bg-secondary d-flex justify-content-between align-items-center">
+        <h5 class="mb-0">📋 Email Journal / Log</h5>
+        <a href="/email-log" class="btn btn-sm btn-outline-light">Vollständiges Log</a>
+      </div>
+      <div class="card-body">
+        <p class="text-muted">
+          Das vollständige Email-Journal zeigt alle verarbeiteten Emails mit Details zu Status, Agent-Zuweisungen und Zeitstempeln.
+        </p>
+      </div>
+    </div>
+  </div>
+</div>
 {% endblock %}
 
 {% block scripts %}