feat(admin): separate platform CRUD from CMS, add entity selector macro

- Move platforms menu from CMS to Platform Admin section with create/edit
- Add platform create page, API endpoint, and service method
- Remove CMS-specific content from platform list and detail pages
- Create shared entity_selector + entity_selected_badge Jinja macros
- Create entity-selector.js generalizing store-selector.js for any entity
- Add Tom Select merchant filter to stores page with localStorage persistence
- Migrate store-products page to use shared macros (remove 53 lines of duped CSS)
- Fix broken icons: puzzle→puzzle-piece, building-storefront→store, language→translate, server→cube

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/templates/shared/macros/inputs.html

@@ -284,6 +284,102 @@
 {% endmacro %}
 
 
+{#
+  Entity Selector (Tom Select)
+  ============================
+  A generic async searchable entity selector using Tom Select.
+  Works for stores, merchants, platforms, or any entity with a search API.
+
+  Includes Tom Select dark mode CSS overrides (no need to add per page).
+
+  Parameters:
+    - ref_name: Alpine.js x-ref name for the select element (default: 'entitySelect')
+    - id: HTML id attribute (default: 'entity-select')
+    - placeholder: Placeholder text (default: 'Search...')
+    - width: CSS width class (default: 'w-80')
+    - label: Accessible label (default: 'Entity selector')
+
+  Usage:
+    {% from 'shared/macros/inputs.html' import entity_selector, entity_selected_badge %}
+
+    {{ entity_selector(ref_name='merchantSelect', id='merchant-select', placeholder='Filter by merchant...') }}
+    {{ entity_selected_badge(entity_var='selectedMerchant', clear_fn='clearMerchantFilter()', color='blue') }}
+#}
+{% macro entity_selector(
+    ref_name='entitySelect',
+    id='entity-select',
+    placeholder='Search...',
+    width='w-80',
+    label='Entity selector'
+) %}
+{# Dark mode CSS is in admin/base.html — no need to duplicate here #}
+<div class="{{ width }}">
+    <select
+        id="{{ id }}"
+        x-ref="{{ ref_name }}"
+        placeholder="{{ placeholder }}"
+        aria-label="{{ label }}"
+    ></select>
+</div>
+{% endmacro %}
+
+
+{#
+  Entity Selected Badge
+  =====================
+  Displays the currently selected entity as a badge with avatar, name, optional code, and clear button.
+
+  Parameters:
+    - entity_var: Alpine.js variable name holding the selected entity (e.g. 'selectedStore')
+    - clear_fn: Alpine.js function to call on clear (e.g. 'clearStoreFilter()')
+    - name_field: Field name for entity name (default: 'name')
+    - code_field: Field name for secondary code display (default: None, omitted if None)
+    - color: Color scheme - 'purple', 'blue', 'teal', 'green' (default: 'purple')
+
+  Usage:
+    {{ entity_selected_badge(
+        entity_var='selectedStore',
+        clear_fn='clearStoreFilter()',
+        code_field='store_code',
+        color='purple'
+    ) }}
+#}
+{% macro entity_selected_badge(
+    entity_var='selectedEntity',
+    clear_fn='clearEntityFilter()',
+    name_field='name',
+    code_field=None,
+    color='purple'
+) %}
+{% set bg = 'bg-' ~ color ~ '-50 dark:bg-' ~ color ~ '-900/20' %}
+{% set border = 'border-' ~ color ~ '-200 dark:border-' ~ color ~ '-800' %}
+{% set avatar_bg = 'bg-' ~ color ~ '-100 dark:bg-' ~ color ~ '-900' %}
+{% set avatar_text = 'text-' ~ color ~ '-600 dark:text-' ~ color ~ '-300' %}
+{% set name_text = 'text-' ~ color ~ '-800 dark:text-' ~ color ~ '-200' %}
+{% set code_text = 'text-' ~ color ~ '-600 dark:text-' ~ color ~ '-400' %}
+{% set btn_text = 'text-' ~ color ~ '-600 dark:text-' ~ color ~ '-400 hover:text-' ~ color ~ '-800 dark:hover:text-' ~ color ~ '-200' %}
+<div x-show="{{ entity_var }}" x-transition class="mb-6 p-3 {{ bg }} rounded-lg border {{ border }}">
+    <div class="flex items-center justify-between">
+        <div class="flex items-center gap-3">
+            <div class="w-8 h-8 rounded-full {{ avatar_bg }} flex items-center justify-center">
+                <span class="text-sm font-semibold {{ avatar_text }}" x-text="{{ entity_var }}?.{{ name_field }}?.charAt(0).toUpperCase()"></span>
+            </div>
+            <div>
+                <span class="font-medium {{ name_text }}" x-text="{{ entity_var }}?.{{ name_field }}"></span>
+                {% if code_field %}
+                <span class="ml-2 text-xs {{ code_text }} font-mono" x-text="{{ entity_var }}?.{{ code_field }}"></span>
+                {% endif %}
+            </div>
+        </div>
+        <button @click="{{ clear_fn }}" class="{{ btn_text }} text-sm flex items-center gap-1">
+            <span x-html="$icon('x', 'w-4 h-4')"></span>
+            Clear filter
+        </button>
+    </div>
+</div>
+{% endmacro %}
+
+
 {#
   Toggle Switch
   =============