Add built-in backup of the data folder (BL-0044)

The reader owns a scheduled backup into BACKUP (Compose: BACKUP_PATH mounted at
/backup, off when unset). A run pauses the scraper queue through its control
API, waits (bounded) until no job is active, writes a verified tar.gz of DATA
with db.json from memory and scraper/queue.json stored paused, excludes
runtime/lock/pid/temp files, resumes only a queue it paused, then applies
count- or day-based retention to its own archive names only. Schedule,
retention, "Back up now" and last result live in Settings > Service health.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/test-compose.js

@@ -6,10 +6,10 @@ const assert = require('assert/strict'), { spawn } = require('child_process');
 const { Canvas } = require('./png');
 const root = path.resolve(__dirname, '..'), dir = fs.mkdtempSync(path.join(os.tmpdir(), 'mc-compose-'));
 const project = 'mc-qa-' + crypto.randomBytes(3).toString('hex'), port = process.env.QA_PORT || '8180';
-const library = path.join(dir, 'library'), data = path.join(dir, 'data'), tokenFile = path.join(dir, 'token');
+const library = path.join(dir, 'library'), data = path.join(dir, 'data'), backupDir = path.join(dir, 'backup'), tokenFile = path.join(dir, 'token');
 const directionQa = process.argv.includes('--direction-ui');
 const peerGatewayQa = process.argv.includes('--peer-gateway');
-fs.mkdirSync(path.join(data, 'scraper'), { recursive: true }); fs.mkdirSync(path.join(data, 'sentinel'));
+fs.mkdirSync(path.join(data, 'scraper'), { recursive: true }); fs.mkdirSync(path.join(data, 'sentinel')); fs.mkdirSync(backupDir);
 if (peerGatewayQa) {
   const peerData = path.join(data, 'peering');
   const peerUsage = path.join(data, 'peering-usage');
@@ -48,7 +48,7 @@ for (const [index, name] of ['Moon Garden', 'Before the Rain', 'Iron Harbor'].en
     status: index ? 'completed' : 'ongoing', tags: ['Fantasy', 'Demo'] }));
 }
 const env = { ...process.env, LIBRARY_PATH: library, DATA_PATH: data, SCRAPER_DATA_PATH: path.join(data, 'scraper'), SENTINEL_DATA_PATH: path.join(data, 'sentinel'),
-  SCRAPER_TOKEN_PATH: tokenFile, READER_PORT: port, READER_BIND: '127.0.0.1', COOKIE_SECURE: '0', APP_IMAGE: process.env.APP_IMAGE || 'mangacircus:local',
+  SCRAPER_TOKEN_PATH: tokenFile, BACKUP_PATH: backupDir, READER_PORT: port, READER_BIND: '127.0.0.1', COOKIE_SECURE: '0', APP_IMAGE: process.env.APP_IMAGE || 'mangacircus:local',
   READER_IMAGE: process.env.APP_IMAGE || 'mangacircus:local',
   ...(readingGateQa ? { READING_WINDOWS_JSON: '{"0":[],"1":[],"2":[],"3":[],"4":[],"5":[],"6":[]}',
     READING_TIMEZONE: 'Europe/Berlin', READING_QUIZ_UNLOCK_MINUTES: '60', READING_QUIZ_CATALOG_PATH: '/data/reading-quiz.json' }
@@ -93,6 +93,14 @@ let keep = false;
     let inventory;
     await until(async () => { inventory = await (await api('/api/library')).json(); return inventory.mangas?.length === 3; }, 'Fixture inventory missing');
     const byTitle = title => inventory.mangas.find(m => m.title === title).id;
+    // Built-in backup through the real control API: archive written, paused queue left paused.
+    const queueBefore = JSON.parse(fs.readFileSync(path.join(data, 'scraper', 'queue.json'), 'utf8'));
+    assert.equal((await api('/api/admin/backup', { command: 'run' })).status, 200);
+    let backupState;
+    await until(async () => { backupState = await (await api('/api/admin/backup')).json(); return backupState.last && !backupState.running; }, 'Backup did not finish');
+    assert.equal(backupState.last.error, undefined, backupState.last.error);
+    assert.ok(fs.existsSync(path.join(backupDir, backupState.last.file)), 'Backup archive missing on the host');
+    assert.equal(JSON.parse(fs.readFileSync(path.join(data, 'scraper', 'queue.json'), 'utf8')).paused, queueBefore.paused);
     if (readingGateQa) {
       const manga = byTitle('Moon Garden'), other = byTitle('Before the Rain');
       const chapter = (await (await api('/api/manga?m=' + encodeURIComponent(manga))).json()).chapters[0].id;
@@ -243,7 +251,7 @@ let keep = false;
     keep = process.argv.includes('--keep');
     if (keep) {
       const envFile = path.join(dir, 'qa.env');
-      fs.writeFileSync(envFile, ['LIBRARY_PATH', 'DATA_PATH', 'SCRAPER_DATA_PATH', 'SENTINEL_DATA_PATH', 'SCRAPER_TOKEN_PATH', 'READER_PORT', 'READER_BIND', 'COOKIE_SECURE', 'APP_IMAGE',
+      fs.writeFileSync(envFile, ['LIBRARY_PATH', 'DATA_PATH', 'SCRAPER_DATA_PATH', 'SENTINEL_DATA_PATH', 'SCRAPER_TOKEN_PATH', 'BACKUP_PATH', 'READER_PORT', 'READER_BIND', 'COOKIE_SECURE', 'APP_IMAGE',
         ...(readingGateQa ? ['READING_WINDOWS_JSON', 'READING_TIMEZONE', 'READING_QUIZ_UNLOCK_MINUTES', 'READING_QUIZ_CATALOG_PATH'] : [])]
         .map(k => `${k}=${k === 'READING_WINDOWS_JSON' ? `'${env[k]}'` : env[k].replaceAll('\\', '/')}`).join('\n') + '\n');
       console.log(JSON.stringify({ project, url, envFile, fixture: dir }));