Feat: add POSIX DB projection

Backend/cmd/posix/main.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+
+	"moku-backend/internal/config"
+	"moku-backend/internal/database"
+	"moku-backend/internal/posixproj"
+)
+
+func main() {
+	command := "rebuild"
+	if len(os.Args) > 1 {
+		command = os.Args[1]
+	}
+
+	switch command {
+	case "rebuild":
+		if err := rebuildProjection(context.Background()); err != nil {
+			log.Fatalf("rebuild POSIX projection: %v", err)
+		}
+	default:
+		log.Fatalf("unsupported posix command %q (supported: rebuild)", command)
+	}
+}
+
+func rebuildProjection(ctx context.Context) error {
+	cfg := config.Load()
+
+	db, err := database.NewPostgres(cfg.PostgresURL)
+	if err != nil {
+		return fmt.Errorf("connect database: %w", err)
+	}
+	defer db.Close()
+
+	summary, err := posixproj.NewProjector(db, cfg.POSIXRoot).RebuildWithSummary(ctx)
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf(
+		"POSIX projection rebuilt from %s\n  total nodes: %d\n  directories: %d\n  files: %d\n",
+		cfg.POSIXRoot,
+		summary.TotalNodes,
+		summary.DirectoryCount,
+		summary.FileCount,
+	)
+	return nil
+}