Wire CI/CD (Gitea Actions typecheck) and daily Postgres backup

- .gitea/workflows/ci.yml runs pnpm typecheck on the already-registered
  forge-runner on push/PR to main
- scripts/backup-db.sh + a systemd user timer (stock-app-backup.timer, daily)
  pg_dump the stocklist Postgres container to ~/backups, pruned to 14 days

scripts/backup-db.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+# Daily pg_dump of the stocklist Postgres container, run by the
+# stock-app-backup systemd timer. Keeps the last 14 days of backups.
+set -euo pipefail
+
+BACKUP_DIR="$HOME/backups/stocklist-postgres"
+mkdir -p "$BACKUP_DIR"
+
+TIMESTAMP=$(date +%Y%m%d-%H%M%S)
+OUT_FILE="$BACKUP_DIR/stocklist-$TIMESTAMP.sql.gz"
+
+docker exec stocklist-postgres pg_dump -U stocklist stocklist | gzip > "$OUT_FILE"
+
+find "$BACKUP_DIR" -name '*.sql.gz' -mtime +14 -delete
+
+echo "Backed up stocklist database to $OUT_FILE"