feat(non-loanable-devices): implement non-loanable device management

- Add non_loanable_devices table to database schema
- Add web interface routes: /non_loanable_devices, /add_non_loanable_device, /edit_non_loanable_device, /delete_non_loanable_device
- Add CLI menu options 8-10 for non-loanable device management
- Add templates for non-loanable device CRUD operations
- Update README.md with new feature documentation
- Update REQUIREMENTS.md marking non-loanable devices as implemented
- Add gestiontablets.sh script

Implements: #porDefinir Registrar nuevos dispositivos no prestables

templates/non_loanable_devices.html

@@ -0,0 +1,43 @@
+{% extends "base.html" %}
+
+{% block content %}
+    <div class="section">
+        <h2>Non-Loanable Devices Inventory</h2>
+        <p>These devices are tracked in inventory but cannot be loaned to users.</p>
+        <a href="/add_non_loanable_device" class="btn">Add Non-Loanable Device</a>
+        
+        {% if devices %}
+            <table>
+                <thead>
+                    <tr>
+                        <th>Type</th>
+                        <th>Brand</th>
+                        <th>Model</th>
+                        <th>Serial Number</th>
+                        <th>Location</th>
+                        <th>Status</th>
+                        <th>Actions</th>
+                    </tr>
+                </thead>
+                <tbody>
+                    {% for device in devices %}
+                        <tr>
+                            <td>{{ device.device_type }}</td>
+                            <td>{{ device.brand }}</td>
+                            <td>{{ device.model }}</td>
+                            <td>{{ device.serial_number }}</td>
+                            <td>{{ device.location or '-' }}</td>
+                            <td>{{ device.status }}</td>
+                            <td>
+                                <a href="/edit_non_loanable_device/{{ device.id }}" class="btn">Edit</a>
+                                <a href="/delete_non_loanable_device/{{ device.id }}" class="btn btn-danger" onclick="return confirm('Are you sure you want to delete this device?')">Delete</a>
+                            </td>
+                        </tr>
+                    {% endfor %}
+                </tbody>
+            </table>
+        {% else %}
+            <p>No non-loanable devices registered.</p>
+        {% endif %}
+    </div>
+{% endblock %}