Add maintenance: purge orphaned source image KV entries

When a source image file is deleted without going through the API
(e.g. the old bin delete bug), the KV entry remains and shows a
broken image. The new maintenance action scans all source image
entries, removes any whose file is missing on disk, and reports
how many were cleaned up.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server.mjs

@@ -3,7 +3,7 @@ process.on('uncaughtException',  (err)    => { console.error('[uncaughtException
 
 import express from 'express';
 import multer from 'multer';
-import { unlinkSync, mkdirSync } from 'node:fs';
+import { unlinkSync, mkdirSync, existsSync } from 'node:fs';
 import { extname, join } from 'node:path';
 import { execFileSync } from 'node:child_process';
 import sharp from 'sharp';
@@ -634,6 +634,18 @@ app.delete('/api/pdfs/:id', (req, res) => {
 // Maintenance
 // ---------------------------------------------------------------------------
 
+app.post('/api/maintenance/purge-missing-sources', (req, res) => {
+	const sources = list_source_images();
+	const removed = [];
+	for (const src of sources) {
+		if (!existsSync(join('./data/images', src.id))) {
+			delete_source_image(src.id);
+			removed.push(src.id);
+		}
+	}
+	ok(res, { removed, total: sources.length });
+});
+
 app.post('/api/maintenance/pdf-thumbs', (req, res) => {
 	const pdfs = list_pdfs();
 	let generated = 0;