fix: add thumbnail cleanup on archive deletion and diagnostic scripts

- Fix archive deletion to also clean up associated thumbnails
- Add cleanup-thumbnails.js script to remove temporary and orphaned thumbnails
- Add diagnose-thumbnails.js script to troubleshoot thumbnail serving issues
- Update README with documentation for new scripts

This prevents thumbnail accumulation when events are deleted and helps
diagnose why thumbnails might not be showing despite existing on disk.

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

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

backend/scripts/cleanup-thumbnails.js

@@ -0,0 +1,107 @@
+#!/usr/bin/env node
+
+/**
+ * Script to clean up orphaned and temporary thumbnails
+ * Usage: node scripts/cleanup-thumbnails.js [--dry-run]
+ */
+
+const path = require('path');
+const fs = require('fs').promises;
+const { db } = require('../src/database/db');
+
+const STORAGE_PATH = process.env.STORAGE_PATH || path.join(__dirname, '../../storage');
+const THUMBNAILS_DIR = path.join(STORAGE_PATH, 'thumbnails');
+
+async function cleanupThumbnails(dryRun = false) {
+  console.log('Starting thumbnail cleanup...');
+  console.log(`Thumbnails directory: ${THUMBNAILS_DIR}`);
+  console.log(`Mode: ${dryRun ? 'DRY RUN' : 'LIVE'}\n`);
+  
+  try {
+    // Get all thumbnail files
+    const files = await fs.readdir(THUMBNAILS_DIR);
+    console.log(`Found ${files.length} files in thumbnails directory`);
+    
+    // Get all valid thumbnail paths from database
+    const validThumbnails = await db('photos')
+      .whereNotNull('thumbnail_path')
+      .select('thumbnail_path');
+    
+    const validPaths = new Set(
+      validThumbnails.map(t => path.basename(t.thumbnail_path))
+    );
+    
+    console.log(`Found ${validPaths.size} valid thumbnails in database\n`);
+    
+    let tempCount = 0;
+    let orphanedCount = 0;
+    let validCount = 0;
+    let deletedCount = 0;
+    
+    for (const file of files) {
+      // Skip directories
+      const filePath = path.join(THUMBNAILS_DIR, file);
+      const stats = await fs.stat(filePath);
+      if (stats.isDirectory()) continue;
+      
+      // Check if it's a temporary file
+      if (file.startsWith('thumb_temp_')) {
+        tempCount++;
+        console.log(`Temporary file: ${file}`);
+        
+        if (!dryRun) {
+          try {
+            await fs.unlink(filePath);
+            deletedCount++;
+          } catch (error) {
+            console.error(`  Failed to delete: ${error.message}`);
+          }
+        }
+      }
+      // Check if it's an orphaned thumbnail
+      else if (!validPaths.has(file)) {
+        orphanedCount++;
+        console.log(`Orphaned file: ${file}`);
+        
+        if (!dryRun) {
+          try {
+            await fs.unlink(filePath);
+            deletedCount++;
+          } catch (error) {
+            console.error(`  Failed to delete: ${error.message}`);
+          }
+        }
+      } else {
+        validCount++;
+      }
+    }
+    
+    console.log('\n--- Summary ---');
+    console.log(`Total files: ${files.length}`);
+    console.log(`Valid thumbnails: ${validCount}`);
+    console.log(`Temporary files: ${tempCount}`);
+    console.log(`Orphaned files: ${orphanedCount}`);
+    if (!dryRun) {
+      console.log(`Deleted files: ${deletedCount}`);
+    } else {
+      console.log(`Files to be deleted: ${tempCount + orphanedCount}`);
+    }
+    
+  } catch (error) {
+    console.error('Error during cleanup:', error);
+    process.exit(1);
+  }
+}
+
+// Parse command line arguments
+const dryRun = process.argv.includes('--dry-run');
+
+// Run the cleanup
+cleanupThumbnails(dryRun).then(async () => {
+  await db.destroy();
+  console.log('\nCleanup complete');
+}).catch(async error => {
+  console.error('Cleanup failed:', error);
+  await db.destroy();
+  process.exit(1);
+});