feat: file manager with browse, search, upload, chmod/chown

- Full file browser page at /files with lazy-load, breadcrumbs, drag&drop
- FileBrowserModal component for path selection from Samba/NFS forms
- PathField component replaces bare inputs in share/export forms
- Backend: /api/files/* routes with List, Mkdir, Rename, Delete, Chmod, Chown, Upload, Download, Preview, Search
- Reuses NASCTL_ALLOWED_ROOTS for path validation
- NASCTL_UPLOAD_MAX_BYTES (100MB) and NASCTL_PREVIEW_MAX_BYTES (256KB) env vars
- Capabilities endpoint returns chmod/chown availability (requires root)
- Version bump: 0.3.2 -> 0.4.0

cmd/nasctl/main.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"strconv"
 	"strings"
 
 	"github.com/darroyo/nasctl/internal/db"
@@ -27,6 +28,8 @@ func main() {
 	adminUser := flag.String("admin-user", envOrDefault("NASCTL_ADMIN_USER", "admin"), "Initial admin username (only used if no admin exists)")
 	adminPass := flag.String("admin-pass", envOrDefault("NASCTL_ADMIN_PASSWORD", "admin"), "Initial admin password (only used if no admin exists)")
 	importOnBoot := flag.Bool("import-on-boot", envOrDefault("NASCTL_IMPORT_ON_BOOT", "false") == "true", "Import existing smb.conf and /etc/exports on first boot")
+	uploadMaxBytes := flag.Int64("upload-max-bytes", parseEnvInt64("NASCTL_UPLOAD_MAX_BYTES", 104857600), "Max bytes for file uploads")
+	previewMaxBytes := flag.Int64("preview-max-bytes", parseEnvInt64("NASCTL_PREVIEW_MAX_BYTES", 262144), "Max bytes for file previews")
 	flag.Parse()
 
 	if err := os.MkdirAll(filepath.Dir(*dbPath), 0o755); err != nil {
@@ -80,10 +83,12 @@ func main() {
 
 	eng := engine.New(sambaModule, nfsModule, usersModule)
 	srv := web.NewServer(database, eng, web.Options{
-		AllowedRoots: parseRoots(*allowedRoots),
-		Auth:         auth,
-		SMBConfPath:  *smbConfPath,
-		ExportsPath:  *exportsPath,
+		AllowedRoots:    parseRoots(*allowedRoots),
+		Auth:            auth,
+		SMBConfPath:     *smbConfPath,
+		ExportsPath:     *exportsPath,
+		UploadMaxBytes:  *uploadMaxBytes,
+		PreviewMaxBytes: *previewMaxBytes,
 	})
 
 	log.Printf("nasctl %s (commit %s) listening on %s (db=%s exec-system=%v)", web.Version, web.Commit, *addr, *dbPath, *execSystem)
@@ -113,3 +118,12 @@ func envOrDefault(key, fallback string) string {
 	}
 	return fallback
 }
+
+func parseEnvInt64(key string, fallback int64) int64 {
+	if value := os.Getenv(key); value != "" {
+		if v, err := strconv.ParseInt(value, 10, 64); err == nil {
+			return v
+		}
+	}
+	return fallback
+}