feat: complete vendor frontend parity with admin

Phase 1 - Sidebar Refactor:
- Refactor sidebar to use collapsible sections with Alpine.js
- Add localStorage persistence for section states
- Reorganize navigation into logical groups

Phase 2 - Core JS Files:
- Add products.js: product CRUD, search, filtering, toggle active/featured
- Add orders.js: order list, status management, filtering
- Add inventory.js: stock tracking, adjust/set quantity modals
- Add customers.js: customer list, order history, messaging
- Add team.js: member invite, role management, remove members
- Add profile.js: profile editing with form validation
- Add settings.js: tabbed settings (general, marketplace, notifications)

Templates updated from placeholders to full functional UIs.
Vendor frontend now at ~90% parity with admin.

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

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

static/vendor/js/init-alpine.js

@@ -9,6 +9,36 @@ const vendorLog = window.LogConfig.log;
 
 console.log('[VENDOR INIT-ALPINE] Loading...');
 
+// Sidebar section state persistence
+const VENDOR_SIDEBAR_STORAGE_KEY = 'vendor_sidebar_sections';
+
+function getVendorSidebarSectionsFromStorage() {
+    try {
+        const stored = localStorage.getItem(VENDOR_SIDEBAR_STORAGE_KEY);
+        if (stored) {
+            return JSON.parse(stored);
+        }
+    } catch (e) {
+        console.warn('[VENDOR INIT-ALPINE] Failed to load sidebar state from localStorage:', e);
+    }
+    // Default: all sections open
+    return {
+        products: true,
+        sales: true,
+        customers: true,
+        shop: true,
+        account: true
+    };
+}
+
+function saveVendorSidebarSectionsToStorage(sections) {
+    try {
+        localStorage.setItem(VENDOR_SIDEBAR_STORAGE_KEY, JSON.stringify(sections));
+    } catch (e) {
+        console.warn('[VENDOR INIT-ALPINE] Failed to save sidebar state to localStorage:', e);
+    }
+}
+
 function data() {
     console.log('[VENDOR INIT-ALPINE] data() function called');
     return {
@@ -21,6 +51,9 @@ function data() {
         vendor: null,
         vendorCode: null,
 
+        // Sidebar collapsible sections state
+        openSections: getVendorSidebarSectionsFromStorage(),
+
         init() {
             // Set current page from URL
             const path = window.location.pathname;
@@ -109,6 +142,12 @@ function data() {
             localStorage.setItem('theme', this.dark ? 'dark' : 'light');
         },
 
+        // Sidebar section toggle with persistence
+        toggleSection(section) {
+            this.openSections[section] = !this.openSections[section];
+            saveVendorSidebarSectionsToStorage(this.openSections);
+        },
+
         async handleLogout() {
             console.log('🚪 Logging out vendor user...');