fix(provisioner): fix collectCPConfigFiles return values

Lines 273 and 276 inside the `if cfg.TemplatePath != ""` block were
returning a bare `error` instead of `(nil, error)`. The enclosing
`collectCPConfigFiles` function returns `(map[string]string, error)`,
so both error returns were missing the `nil` first value — causing
compile failures:

    cp_provisioner.go:273: not enough return values
    cp_provisioner.go:276: not enough return values

Fix: prefix both with `nil, `.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workspace-server/internal/provisioner/cp_provisioner.go

@@ -270,10 +270,10 @@ func collectCPConfigFiles(cfg WorkspaceConfig) (map[string]string, error) {
 		// would bypass the subsequent path-relativization checks below.
 		rootInfo, err := os.Lstat(cfg.TemplatePath)
 		if err != nil {
-			return fmt.Errorf("collectCPConfigFiles: lstat template path: %w", err)
+			return nil, fmt.Errorf("collectCPConfigFiles: lstat template path: %w", err)
 		}
 		if rootInfo.Mode()&os.ModeSymlink != 0 {
-			return fmt.Errorf("collectCPConfigFiles: template path must not be a symlink")
+			return nil, fmt.Errorf("collectCPConfigFiles: template path must not be a symlink")
 		}
 		err = filepath.WalkDir(cfg.TemplatePath, func(path string, d os.DirEntry, walkErr error) error {
 			if walkErr != nil {