fix(db): Open 自动创建父目录（自定义 DATA_DIR 首启不报错）；add docker-compose.dev.yml（PG+pgvector 必需 + Ollama embedding 可选）

internal/db/db.go

@@ -22,6 +22,8 @@ import (
 	"fmt"
 	"io"
 	"log/slog"
+	"os"
+	"path/filepath"
 	"strings"
 
 	_ "modernc.org/sqlite" // pure-Go SQLite driver, registers driver name "sqlite"
@@ -66,6 +68,16 @@ func Open(ctx context.Context, path string, log *slog.Logger) (*sql.DB, error) {
 	}
 	log = discardLogger(log)
 
+	// Ensure the parent directory exists for file-backed databases so a custom
+	// DATA_DIR (e.g. ./data) works on first run without a pre-made directory.
+	if !isMemory(path) {
+		if dir := filepath.Dir(path); dir != "" && dir != "." {
+			if err := os.MkdirAll(dir, 0o755); err != nil {
+				return nil, fmt.Errorf("db: create dir %q: %w", dir, err)
+			}
+		}
+	}
+
 	db, err := sql.Open("sqlite", buildDSN(path))
 	if err != nil {
 		return nil, fmt.Errorf("db: open %q: %w", path, err)