feat: add vendor notifications and analytics pages (Phase 3)

New pages:
- Notifications center: view, mark read, delete, settings modal
- Analytics: period selector, stats overview, feature-gated advanced metrics

Changes:
- Add routes for /vendor/{code}/notifications and /analytics
- Create notifications.js and analytics.js with full functionality
- Create notifications.html and analytics.html templates
- Update sidebar with Analytics link and Notifications in Customers section
- Update vendor-frontend-parity-plan.md to mark Phase 3 complete

Vendor frontend now at ~95% 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/analytics.js

@@ -0,0 +1,199 @@
+// static/vendor/js/analytics.js
+/**
+ * Vendor analytics and reports page logic
+ * View business metrics and performance data
+ */
+
+const vendorAnalyticsLog = window.LogConfig.loggers.vendorAnalytics ||
+    window.LogConfig.createLogger('vendorAnalytics', false);
+
+vendorAnalyticsLog.info('Loading...');
+
+function vendorAnalytics() {
+    vendorAnalyticsLog.info('vendorAnalytics() called');
+
+    return {
+        // Inherit base layout state
+        ...data(),
+
+        // Set page identifier
+        currentPage: 'analytics',
+
+        // Loading states
+        loading: true,
+        error: '',
+
+        // Time period
+        period: '30d',
+        periodOptions: [
+            { value: '7d', label: 'Last 7 Days' },
+            { value: '30d', label: 'Last 30 Days' },
+            { value: '90d', label: 'Last 90 Days' },
+            { value: '1y', label: 'Last Year' }
+        ],
+
+        // Analytics data
+        analytics: null,
+        stats: null,
+
+        // Dashboard stats (from vendor stats endpoint)
+        dashboardStats: {
+            total_products: 0,
+            active_products: 0,
+            featured_products: 0,
+            total_orders: 0,
+            pending_orders: 0,
+            total_customers: 0,
+            total_inventory: 0,
+            low_stock_count: 0
+        },
+
+        async init() {
+            vendorAnalyticsLog.info('Analytics init() called');
+
+            // Guard against multiple initialization
+            if (window._vendorAnalyticsInitialized) {
+                vendorAnalyticsLog.warn('Already initialized, skipping');
+                return;
+            }
+            window._vendorAnalyticsInitialized = true;
+
+            try {
+                await this.loadAllData();
+            } catch (error) {
+                vendorAnalyticsLog.error('Init failed:', error);
+                this.error = 'Failed to initialize analytics page';
+            } finally {
+                this.loading = false;
+            }
+
+            vendorAnalyticsLog.info('Analytics initialization complete');
+        },
+
+        /**
+         * Load all analytics data
+         */
+        async loadAllData() {
+            this.loading = true;
+            this.error = '';
+
+            try {
+                // Load analytics and stats in parallel
+                const [analyticsResponse, statsResponse] = await Promise.all([
+                    this.fetchAnalytics(),
+                    this.fetchStats()
+                ]);
+
+                this.analytics = analyticsResponse;
+                this.dashboardStats = statsResponse;
+
+                vendorAnalyticsLog.info('Loaded analytics data');
+            } catch (error) {
+                vendorAnalyticsLog.error('Failed to load data:', error);
+                this.error = error.message || 'Failed to load analytics data';
+            } finally {
+                this.loading = false;
+            }
+        },
+
+        /**
+         * Fetch analytics data for current period
+         */
+        async fetchAnalytics() {
+            try {
+                const response = await apiClient.get(`/vendor/${this.vendorCode}/analytics?period=${this.period}`);
+                return response;
+            } catch (error) {
+                // Analytics might require feature access
+                if (error.status === 403) {
+                    vendorAnalyticsLog.warn('Analytics feature not available');
+                    return null;
+                }
+                throw error;
+            }
+        },
+
+        /**
+         * Fetch dashboard stats
+         */
+        async fetchStats() {
+            try {
+                const response = await apiClient.get(`/vendor/${this.vendorCode}/dashboard/stats`);
+                return {
+                    total_products: response.catalog?.total_products || 0,
+                    active_products: response.catalog?.active_products || 0,
+                    featured_products: response.catalog?.featured_products || 0,
+                    total_orders: response.orders?.total || 0,
+                    pending_orders: response.orders?.pending || 0,
+                    total_customers: response.customers?.total || 0,
+                    total_inventory: response.inventory?.total_quantity || 0,
+                    low_stock_count: response.inventory?.low_stock_count || 0
+                };
+            } catch (error) {
+                vendorAnalyticsLog.error('Failed to fetch stats:', error);
+                return this.dashboardStats;
+            }
+        },
+
+        /**
+         * Change time period and reload data
+         */
+        async changePeriod(newPeriod) {
+            this.period = newPeriod;
+            await this.loadAllData();
+        },
+
+        /**
+         * Get period label
+         */
+        getPeriodLabel() {
+            const option = this.periodOptions.find(p => p.value === this.period);
+            return option ? option.label : this.period;
+        },
+
+        /**
+         * Format number with commas
+         */
+        formatNumber(num) {
+            if (num === null || num === undefined) return '0';
+            return num.toLocaleString();
+        },
+
+        /**
+         * Format percentage
+         */
+        formatPercent(value) {
+            if (value === null || value === undefined) return '0%';
+            return `${value.toFixed(1)}%`;
+        },
+
+        /**
+         * Calculate active product percentage
+         */
+        get activeProductPercent() {
+            if (!this.dashboardStats.total_products) return 0;
+            return (this.dashboardStats.active_products / this.dashboardStats.total_products * 100).toFixed(1);
+        },
+
+        /**
+         * Calculate pending order percentage
+         */
+        get pendingOrderPercent() {
+            if (!this.dashboardStats.total_orders) return 0;
+            return (this.dashboardStats.pending_orders / this.dashboardStats.total_orders * 100).toFixed(1);
+        },
+
+        /**
+         * Get stock health status
+         */
+        get stockHealth() {
+            if (this.dashboardStats.low_stock_count === 0) {
+                return { status: 'good', label: 'Healthy', color: 'green' };
+            } else if (this.dashboardStats.low_stock_count <= 5) {
+                return { status: 'warning', label: 'Attention Needed', color: 'yellow' };
+            } else {
+                return { status: 'critical', label: 'Critical', color: 'red' };
+            }
+        }
+    };
+}