DB resilience: hourly WAL checkpoint + daily rolling 7-day backup

- Hourly PASSIVE WAL checkpoint prevents unbounded WAL growth and
  ensures all writes are merged into the main .db file regularly.
  Previously the WAL was never checkpointed — all data was accumulating
  in stories.db-wal with no protection if that file was lost.
- Daily backup using better-sqlite3 .backup() writes a safe online
  snapshot to data/backups/stories-YYYY-MM-DD.db on startup and
  every 24 h; keeps last 7 days, pruning older ones automatically.
- busy_timeout = 5000 so concurrent requests wait briefly rather
  than failing with SQLITE_BUSY.

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

server/db.js

@@ -1,5 +1,5 @@
 import Database from 'better-sqlite3'
-import { mkdirSync } from 'fs'
+import { mkdirSync, readdirSync, unlinkSync } from 'fs'
 import path from 'path'
 import { fileURLToPath } from 'url'
 
@@ -10,6 +10,42 @@ mkdirSync(dataDir, { recursive: true })
 const db = new Database(path.join(dataDir, 'stories.db'))
 db.pragma('journal_mode = WAL')
 db.pragma('foreign_keys = ON')
+db.pragma('busy_timeout = 5000')    // wait up to 5 s instead of failing immediately
+
+// Merge the WAL back into the main DB file once an hour.
+// Without this, all writes live in the WAL indefinitely, and losing
+// that file means losing all data written since the last checkpoint.
+setInterval(() => {
+  try { db.pragma('wal_checkpoint(PASSIVE)') }
+  catch (err) { console.warn('[db] WAL checkpoint failed:', err.message) }
+}, 60 * 60 * 1000)   // every hour
+
+// Daily backup — keeps the last 7 daily snapshots in data/backups/
+const backupDir = path.join(dataDir, 'backups')
+mkdirSync(backupDir, { recursive: true })
+
+async function runBackup() {
+  try {
+    const stamp = new Date().toISOString().slice(0, 10)   // YYYY-MM-DD
+    const dest  = path.join(backupDir, `stories-${stamp}.db`)
+    await db.backup(dest)
+    console.log(`[db] Backup written → ${dest}`)
+
+    // Prune backups older than 7 days
+    const files = readdirSync(backupDir)
+      .filter(f => f.startsWith('stories-') && f.endsWith('.db'))
+      .sort()
+    for (const old of files.slice(0, -7)) {
+      try { unlinkSync(path.join(backupDir, old)) } catch {}
+    }
+  } catch (err) {
+    console.warn('[db] Backup failed:', err.message)
+  }
+}
+
+// Run once on startup, then every 24 h
+runBackup()
+setInterval(runBackup, 24 * 60 * 60 * 1000)
 
 db.exec(`
   CREATE TABLE IF NOT EXISTS users (