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/admin/js/code-quality-violations.js

@@ -20,9 +20,9 @@ function codeQualityViolations() {
         violations: [],
         pagination: {
             page: 1,
-            page_size: 50,
+            per_page: 20,
             total: 0,
-            total_pages: 0
+            pages: 0
         },
         filters: {
             validator_type: '',
@@ -33,6 +33,18 @@ function codeQualityViolations() {
         },
 
         async init() {
+            // Guard against multiple initialization
+            if (window._codeQualityViolationsInitialized) {
+                codeQualityViolationsLog.warn('Already initialized, skipping');
+                return;
+            }
+            window._codeQualityViolationsInitialized = true;
+
+            // Load platform settings for rows per page
+            if (window.PlatformSettings) {
+                this.pagination.per_page = await window.PlatformSettings.getRowsPerPage();
+            }
+
             // Load filters from URL params
             const params = new URLSearchParams(window.location.search);
             this.filters.validator_type = params.get('validator_type') || '';
@@ -52,7 +64,7 @@ function codeQualityViolations() {
                 // Build query params
                 const params = {
                     page: this.pagination.page.toString(),
-                    page_size: this.pagination.page_size.toString()
+                    page_size: this.pagination.per_page.toString()
                 };
 
                 if (this.filters.validator_type) params.validator_type = this.filters.validator_type;
@@ -64,12 +76,8 @@ function codeQualityViolations() {
                 const data = await apiClient.get('/admin/code-quality/violations', params);
 
                 this.violations = data.violations;
-                this.pagination = {
-                    page: data.page,
-                    page_size: data.page_size,
-                    total: data.total,
-                    total_pages: data.total_pages
-                };
+                this.pagination.total = data.total;
+                this.pagination.pages = data.total_pages;
 
                 // Update URL with current filters (without reloading)
                 this.updateURL();
@@ -93,7 +101,7 @@ function codeQualityViolations() {
         },
 
         async nextPage() {
-            if (this.pagination.page < this.pagination.total_pages) {
+            if (this.pagination.page < this.pagination.pages) {
                 this.pagination.page++;
                 await this.loadViolations();
             }
@@ -101,18 +109,18 @@ function codeQualityViolations() {
 
         // Computed: Total number of pages
         get totalPages() {
-            return this.pagination.total_pages;
+            return this.pagination.pages;
         },
 
         // Computed: Start index for pagination display
         get startIndex() {
             if (this.pagination.total === 0) return 0;
-            return (this.pagination.page - 1) * this.pagination.page_size + 1;
+            return (this.pagination.page - 1) * this.pagination.per_page + 1;
         },
 
         // Computed: End index for pagination display
         get endIndex() {
-            const end = this.pagination.page * this.pagination.page_size;
+            const end = this.pagination.page * this.pagination.per_page;
             return end > this.pagination.total ? this.pagination.total : end;
         },