Keep the database in ./data and bind-mount it

SQLite writes three files — the database plus its -wal and -shm companions.
Putting them in one directory means a deployment mounts a single path and a
backup copies a single directory.

- FOODSTER_DB defaults to ./data/foodster.db, and openDB creates the parent
  directory on startup rather than failing on a fresh checkout
- compose bind-mounts ./data instead of using a named volume, so the file can
  be listed, copied and opened with any sqlite client without going through
  the container engine
- the image runs as UID 65534, which cannot write to a host directory owned
  by someone else, so compose now sets user: from FOODSTER_UID/FOODSTER_GID
- `make up` creates ./data first: left to the engine it appears root-owned
  and the app silently cannot write to it

cmd/foodster/main.go

@@ -18,6 +18,7 @@ import (
 	"net/http"
 	"os"
 	"os/signal"
+	"path/filepath"
 	"strings"
 	"syscall"
 	"time"
@@ -36,7 +37,10 @@ var version = "dev"
 const (
 	listenAddr = ":8080"
 	defaultTZ  = "Europe/Helsinki"
-	defaultDB  = "./foodster.db"
+	// Everything SQLite writes — the database plus its -wal and -shm
+	// companions — lives in one directory, so a deployment mounts a single
+	// path and a backup copies a single directory.
+	defaultDB = "./data/foodster.db"
 
 	// failDelay throttles password guessing.
 	// ponytail: a fixed sleep is enough for a LAN-only app; swap in
@@ -108,6 +112,12 @@ func run() error {
 
 // openDB opens the SQLite file and brings its schema up to date.
 func openDB(path string) (*sql.DB, error) {
+	if dir := filepath.Dir(path); dir != "." && dir != "" {
+		if err := os.MkdirAll(dir, 0o755); err != nil {
+			return nil, fmt.Errorf("create %s: %w", dir, err)
+		}
+	}
+
 	dsn := "file:" + path +
 		"?_pragma=journal_mode(WAL)" +
 		"&_pragma=foreign_keys(ON)" +