Fix elevation overlap, add device images, rack merge, and size override

- Fix elevation rendering bug: device blocks were drawn MARGIN px
  further right than the rack frame/unit slots, causing them to
  overlap and extend past the right border. All three now share one
  RACK_X origin.
- Show the device type's front/rear image inside each elevation block
  (clipped to the block, translucent label bar on top for legibility)
  when one is set on the device type; falls back to a plain colour
  block with text otherwise.
- Add "Merge" action to combine two concepts into one taller one (e.g.
  two half-height racks stacked into a full-height rack): the top
  concept's devices are shifted up by the bottom concept's height,
  neither source is modified. Available from the plugin menu, from a
  concept's detail page, and via POST /concepts/merge/.
- Copying a real rack into a concept can now target a different width,
  height and/or starting unit than the source rack; devices that no
  longer fit at the chosen size are skipped and reported as warnings
  instead of aborting the copy.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

netbox_rack_concept/templates/netbox_rack_concept/concept_merge.html

@@ -0,0 +1,28 @@
+{% extends 'base/layout.html' %}
+{% load i18n %}
+{% load form_helpers %}
+
+{% block title %}{% trans "Merge Rack Concepts" %}{% endblock %}
+
+{% block content %}
+<form action="" method="post">
+  {% csrf_token %}
+  <div class="row">
+    <div class="col col-md-8 offset-md-2">
+      <div class="card">
+        <h2 class="card-header">{% trans "Merge two concepts into one" %}</h2>
+        <div class="card-body">
+          <p class="text-muted">
+            {% trans "Stacks the bottom concept's devices unchanged and shifts the top concept's devices up by the bottom concept's height, into one new, taller blueprint. Neither source concept is modified." %}
+          </p>
+          {% render_form form %}
+        </div>
+        <div class="card-footer text-end">
+          <a href="{{ return_url }}" class="btn btn-outline-danger">{% trans "Cancel" %}</a>
+          <button type="submit" class="btn btn-primary">{% trans "Merge" %}</button>
+        </div>
+      </div>
+    </div>
+  </div>
+</form>
+{% endblock %}

netbox_rack_concept/templates/netbox_rack_concept/inc/elevation.html

@@ -15,11 +15,11 @@
     {# Unit rows and legend #}
     {% for unit in elevation.units %}
       <g class="unit">
-        <rect x="{{ elevation.legend_width }}" y="{{ unit.y }}"
+        <rect x="{{ elevation.rack_x }}" y="{{ unit.y }}"
               width="{{ elevation.rack_width }}" height="{{ unit.height }}"
               class="unit-slot"
               data-unit="{{ unit.number }}"></rect>
-        <text x="{{ elevation.legend_width }}" y="{{ unit.y }}" dx="-4" dy="15"
+        <text x="{{ elevation.rack_x }}" y="{{ unit.y }}" dx="-4" dy="15"
               class="unit-label" text-anchor="end">{{ unit.number }}</text>
       </g>
     {% endfor %}
@@ -32,13 +32,31 @@
          data-u-height="{{ block.device.effective_u_height }}"
          data-width-fraction="{{ block.device.width_fraction }}">
         <a href="{{ block.device.get_absolute_url }}">
+          {% if block.image %}
+            <clipPath id="concept-block-{{ elevation.face }}-{{ block.device.pk }}">
+              <rect x="{{ block.x }}" y="{{ block.y }}" width="{{ block.width }}" height="{{ block.height }}" rx="2"></rect>
+            </clipPath>
+          {% endif %}
           <rect x="{{ block.x }}" y="{{ block.y }}" width="{{ block.width }}" height="{{ block.height }}"
                 rx="2" fill="#{{ block.color }}"
                 fill-opacity="{% if block.opposite %}0.35{% else %}1{% endif %}"
                 class="device-rect"></rect>
+          {% if block.image %}
+            <image href="{{ block.image.url }}" x="{{ block.x }}" y="{{ block.y }}"
+                   width="{{ block.width }}" height="{{ block.height }}"
+                   preserveAspectRatio="xMidYMid slice"
+                   clip-path="url(#concept-block-{{ elevation.face }}-{{ block.device.pk }})"
+                   opacity="{% if block.opposite %}0.35{% else %}1{% endif %}"
+                   class="device-image"></image>
+          {% endif %}
           {% if block.show_text %}
+            {% if block.image %}
+              <rect x="{{ block.x }}" y="{{ block.y }}" width="{{ block.width }}" height="16"
+                    class="device-label-bg"></rect>
+            {% endif %}
             <text x="{{ block.x }}" y="{{ block.y }}" dy="15" dx="6"
-                  fill="#{{ block.text_color }}" class="device-label">
+                  fill="{% if block.image %}#ffffff{% else %}#{{ block.text_color }}{% endif %}"
+                  class="device-label {% if block.image %}on-image{% endif %}">
               {{ block.label }}{% if block.opposite %} <tspan class="opposite-hint">({% trans "rear" %})</tspan>{% endif %}
             </text>
           {% endif %}
@@ -47,7 +65,7 @@
       </g>
     {% endfor %}
 
-    <rect x="{{ elevation.legend_width }}" y="6"
+    <rect x="{{ elevation.rack_x }}" y="6"
           width="{{ elevation.rack_width }}" height="{{ elevation.height|add:'-12' }}"
           class="rack-frame" fill="none"></rect>
   </svg>

netbox_rack_concept/templates/netbox_rack_concept/rackconcept.html

@@ -15,6 +15,9 @@
     <a href="{% url 'plugins:netbox_rack_concept:rackconcept_clone_concept' pk=object.pk %}" class="btn btn-outline-secondary">
       <i class="mdi mdi-content-duplicate"></i> {% trans "Clone concept" %}
     </a>
+    <a href="{% url 'plugins:netbox_rack_concept:rackconcept_merge' %}?concept_bottom={{ object.pk }}" class="btn btn-outline-secondary">
+      <i class="mdi mdi-call-merge"></i> {% trans "Merge with another" %}
+    </a>
   {% endif %}
   {% if perms.dcim.add_rack %}
     <a href="{% url 'plugins:netbox_rack_concept:rackconcept_deploy' pk=object.pk %}" class="btn btn-primary">