feat: phone webhook integration (callstart/callend on port 8081)

- New webhook server on port 8081 for phone system (PBX)
- Endpoints: GET/POST /{extension}/callstart and /{extension}/callend
- New 'phone_extension' field on users (Durchwahl)
- Only activates when user is anwesend or homeoffice (AIDA)
- Sets WLED to phone_active color (red) on callstart
- Restores previous Teams/AIDA color on callend
- Polling skips WLED update while phone is active
- Dashboard shows phone badge when user is in a call
- New color rule 'phone_active' (configurable via web UI)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

templates/dashboard.html

@@ -81,6 +81,10 @@
                                     <span class="badge bg-light text-dark"><i class="bi bi-microsoft-teams"></i> {{ seg.teams }}</span>
                                 {% endif %}
                             {% endif %}
+
+                            {% if seg.phone %}
+                                <span class="badge bg-danger"><i class="bi bi-telephone-fill"></i> Telefoniert</span>
+                            {% endif %}
                         </div>
                         {% endif %}
                     {% else %}