feat: add update instructions dialog, email notifications, and capture date sorting

- Add Update Instructions Dialog with environment-specific commands (Docker/Git/Standalone)
- Add email notification settings for new version alerts
- Add "Sort by Capture Date" option using EXIF metadata extraction
- Fix E2E tests by loading environment variables via dotenv
- Add test-images/ and backend/*.db to .gitignore

Closes #181

backend/src/services/updateNotificationService.js

@@ -0,0 +1,246 @@
+/**
+ * Update Notification Service
+ * Checks for updates and sends email notifications to administrators.
+ */
+
+const { db } = require('../database/db');
+const { checkForUpdates } = require('./updateCheckService');
+const { sendTemplateEmail, initializeTransporter } = require('./emailProcessor');
+const logger = require('../utils/logger');
+
+/**
+ * Get update notification settings from database
+ */
+async function getUpdateNotificationSettings() {
+  try {
+    const settings = await db('app_settings')
+      .whereIn('setting_key', [
+        'update_email_notifications_enabled',
+        'update_email_recipients',
+        'last_notified_version'
+      ])
+      .select('setting_key', 'setting_value');
+
+    const result = {};
+    for (const setting of settings) {
+      try {
+        result[setting.setting_key] = JSON.parse(setting.setting_value);
+      } catch (e) {
+        result[setting.setting_key] = setting.setting_value;
+      }
+    }
+
+    return {
+      enabled: result.update_email_notifications_enabled === true,
+      recipients: result.update_email_recipients || '',
+      lastNotifiedVersion: result.last_notified_version || ''
+    };
+  } catch (error) {
+    logger.error('Error fetching update notification settings:', error);
+    return {
+      enabled: false,
+      recipients: '',
+      lastNotifiedVersion: ''
+    };
+  }
+}
+
+/**
+ * Update the last notified version in database
+ */
+async function updateLastNotifiedVersion(version) {
+  try {
+    await db('app_settings')
+      .where('setting_key', 'last_notified_version')
+      .update({
+        setting_value: JSON.stringify(version),
+        updated_at: db.fn.now()
+      });
+  } catch (error) {
+    logger.error('Error updating last notified version:', error);
+  }
+}
+
+/**
+ * Get admin email addresses to notify
+ * If recipients setting is empty, get all active admin emails
+ */
+async function getNotificationRecipients(recipientsSetting) {
+  try {
+    if (recipientsSetting && recipientsSetting.trim()) {
+      // Use configured recipients (comma-separated)
+      return recipientsSetting.split(',').map(email => email.trim()).filter(Boolean);
+    }
+
+    // Fallback: get all active admin user emails
+    const admins = await db('admin_users')
+      .where('is_active', true)
+      .whereNotNull('email')
+      .select('email');
+
+    return admins.map(admin => admin.email).filter(Boolean);
+  } catch (error) {
+    logger.error('Error fetching notification recipients:', error);
+    return [];
+  }
+}
+
+/**
+ * Check for updates and send notification emails if new version is available
+ */
+async function checkAndNotifyUpdates() {
+  logger.info('Update notification service: Checking for updates...');
+
+  try {
+    // Check if update notifications are enabled
+    const settings = await getUpdateNotificationSettings();
+
+    if (!settings.enabled) {
+      logger.info('Update email notifications are disabled');
+      return { notified: false, reason: 'notifications_disabled' };
+    }
+
+    // Check for available updates
+    const updateInfo = await checkForUpdates();
+
+    if (!updateInfo.updateAvailable) {
+      logger.info('No updates available');
+      return { notified: false, reason: 'no_updates' };
+    }
+
+    const newVersion = updateInfo.latest.forChannel;
+
+    // Check if we've already notified about this version
+    if (settings.lastNotifiedVersion === newVersion) {
+      logger.info(`Already notified about version ${newVersion}`);
+      return { notified: false, reason: 'already_notified' };
+    }
+
+    // Get recipients
+    const recipients = await getNotificationRecipients(settings.recipients);
+
+    if (recipients.length === 0) {
+      logger.warn('No recipients configured for update notifications');
+      return { notified: false, reason: 'no_recipients' };
+    }
+
+    // Ensure email transporter is initialized
+    await initializeTransporter();
+
+    // Send email to each recipient
+    const frontendUrl = process.env.FRONTEND_URL || 'http://localhost:3000';
+    const releaseNotesUrl = `https://github.com/the-luap/picpeak/releases/tag/v${newVersion}`;
+    const channelLabel = updateInfo.channel === 'beta' ? 'Beta' : 'Stable';
+
+    let successCount = 0;
+    let errorCount = 0;
+
+    for (const email of recipients) {
+      try {
+        await sendTemplateEmail(email, 'version_update_available', {
+          current_version: updateInfo.current,
+          new_version: newVersion,
+          channel: channelLabel,
+          release_notes_url: releaseNotesUrl,
+          admin_url: `${frontendUrl}/admin`
+        });
+        successCount++;
+        logger.info(`Update notification sent to ${email}`);
+      } catch (error) {
+        errorCount++;
+        logger.error(`Failed to send update notification to ${email}:`, error);
+      }
+    }
+
+    // Update last notified version
+    if (successCount > 0) {
+      await updateLastNotifiedVersion(newVersion);
+      logger.info(`Update notifications sent: ${successCount} success, ${errorCount} failed`);
+    }
+
+    return {
+      notified: successCount > 0,
+      newVersion,
+      successCount,
+      errorCount,
+      totalRecipients: recipients.length
+    };
+  } catch (error) {
+    logger.error('Error in update notification service:', error);
+    return { notified: false, reason: 'error', error: error.message };
+  }
+}
+
+/**
+ * Force send update notification (for manual trigger from admin UI)
+ */
+async function sendUpdateNotificationNow() {
+  logger.info('Manually triggering update notification...');
+
+  try {
+    // Check for available updates
+    const updateInfo = await checkForUpdates(true); // Force refresh
+
+    if (!updateInfo.updateAvailable) {
+      return { success: false, message: 'No updates available' };
+    }
+
+    const newVersion = updateInfo.latest.forChannel;
+    const settings = await getUpdateNotificationSettings();
+
+    // Get recipients
+    const recipients = await getNotificationRecipients(settings.recipients);
+
+    if (recipients.length === 0) {
+      return { success: false, message: 'No recipients configured' };
+    }
+
+    // Ensure email transporter is initialized
+    await initializeTransporter();
+
+    // Send email to each recipient
+    const releaseNotesUrl = `https://github.com/the-luap/picpeak/releases/tag/v${newVersion}`;
+    const channelLabel = updateInfo.channel === 'beta' ? 'Beta' : 'Stable';
+
+    let successCount = 0;
+    let errorCount = 0;
+
+    for (const email of recipients) {
+      try {
+        await sendTemplateEmail(email, 'version_update_available', {
+          current_version: updateInfo.current,
+          new_version: newVersion,
+          channel: channelLabel,
+          release_notes_url: releaseNotesUrl
+        });
+        successCount++;
+      } catch (error) {
+        errorCount++;
+        logger.error(`Failed to send update notification to ${email}:`, error);
+      }
+    }
+
+    // Update last notified version
+    if (successCount > 0) {
+      await updateLastNotifiedVersion(newVersion);
+    }
+
+    return {
+      success: successCount > 0,
+      newVersion,
+      successCount,
+      errorCount,
+      totalRecipients: recipients.length
+    };
+  } catch (error) {
+    logger.error('Error sending manual update notification:', error);
+    return { success: false, message: error.message };
+  }
+}
+
+module.exports = {
+  checkAndNotifyUpdates,
+  sendUpdateNotificationNow,
+  getUpdateNotificationSettings,
+  getNotificationRecipients
+};