feat: add PlatformSettings for pagination and vendor filter improvements

Platform Settings:
- Add PlatformSettings utility in init-alpine.js with 5-min cache
- Add Display tab in /admin/settings for rows_per_page config
- Integrate PlatformSettings.getRowsPerPage() in all paginated pages
- Standardize default per_page to 20 across all admin pages
- Add documentation at docs/frontend/shared/platform-settings.md

Architecture Rules:
- Add JS-010: enforce PlatformSettings usage for pagination
- Add JS-011: enforce standard pagination structure
- Add JS-012: detect double /api/v1 prefix in apiClient calls
- Implement all rules in validate_architecture.py

Vendor Filter (Tom Select):
- Add vendor filter to marketplace-products, vendor-products,
  customers, inventory, and vendor-themes pages
- Add selectedVendor display panel with clear button
- Add localStorage persistence for vendor selection
- Fix double /api/v1 prefix in vendor-selector.js

Bug Fixes:
- Remove duplicate PlatformSettings from utils.js
- Fix customers.js pagination structure (page_size → per_page)
- Fix code-quality-violations.js pagination structure

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

static/shared/js/utils.js

@@ -187,83 +187,8 @@ const Utils = {
 // ============================================================================
 // Platform Settings
 // ============================================================================
-
-/**
- * Platform settings cache and loader
- */
-const PlatformSettings = {
-    _settings: null,
-    _loading: false,
-    _loadPromise: null,
-
-    /**
-     * Load platform display settings from API
-     * @returns {Promise<Object>} Platform settings
-     */
-    async load() {
-        // Return cached settings if available
-        if (this._settings) {
-            return this._settings;
-        }
-
-        // Return existing promise if already loading
-        if (this._loadPromise) {
-            return this._loadPromise;
-        }
-
-        this._loading = true;
-        this._loadPromise = (async () => {
-            try {
-                const response = await fetch('/api/v1/admin/settings/display/public');
-                if (response.ok) {
-                    this._settings = await response.json();
-                } else {
-                    // Default settings
-                    this._settings = { rows_per_page: 20 };
-                }
-            } catch (error) {
-                console.warn('Failed to load platform settings, using defaults:', error);
-                this._settings = { rows_per_page: 20 };
-            }
-            this._loading = false;
-            return this._settings;
-        })();
-
-        return this._loadPromise;
-    },
-
-    /**
-     * Get rows per page setting
-     * @returns {number} Rows per page (default: 20)
-     */
-    getRowsPerPage() {
-        return this._settings?.rows_per_page || 20;
-    },
-
-    /**
-     * Get rows per page synchronously (returns cached or default)
-     * @returns {number} Rows per page
-     */
-    get rowsPerPage() {
-        return this._settings?.rows_per_page || 20;
-    },
-
-    /**
-     * Reset cached settings (call after updating settings)
-     */
-    reset() {
-        this._settings = null;
-        this._loadPromise = null;
-    }
-};
-
-// Load settings on page load
-document.addEventListener('DOMContentLoaded', () => {
-    PlatformSettings.load();
-});
-
 // Make available globally
-window.PlatformSettings = PlatformSettings;
+// Note: PlatformSettings is defined in init-alpine.js for admin pages
 window.Utils = Utils;
 
 // Export for modules

static/shared/js/vendor-selector.js

@@ -66,7 +66,7 @@ function waitForTomSelect(callback, maxRetries = 20, retryDelay = 100) {
  * @param {number} options.minChars - Minimum characters before search (default: 2)
  * @param {number} options.maxOptions - Maximum options to show (default: 50)
  * @param {string} options.placeholder - Placeholder text
- * @param {string} options.apiEndpoint - API endpoint for search (default: '/api/v1/admin/vendors')
+ * @param {string} options.apiEndpoint - API endpoint for search (default: '/admin/vendors')
  * @returns {Object} Controller object with setValue() and clear() methods
  */
 function initVendorSelector(selectElement, options = {}) {
@@ -79,7 +79,7 @@ function initVendorSelector(selectElement, options = {}) {
         minChars: options.minChars || 2,
         maxOptions: options.maxOptions || 50,
         placeholder: options.placeholder || selectElement.getAttribute('placeholder') || 'Search vendor by name or code...',
-        apiEndpoint: options.apiEndpoint || '/api/v1/admin/vendors',
+        apiEndpoint: options.apiEndpoint || '/admin/vendors',  // Note: apiClient adds /api/v1 prefix
         onSelect: options.onSelect || (() => {}),
         onClear: options.onClear || (() => {})
     };