🤖 feat: load plugin env from secret files

What:
- read plugin env values from files when paths exist

Why:
- support requiredEnv secrets without embedding values in Nix

Tests:
- nix flake check

Author: DJTBOT

nix/modules/home-manager/openclaw/config.nix

@@ -83,7 +83,13 @@ let
         export PATH="${lib.makeBinPath pluginPackages}:$PATH"
       fi
 
-      ${lib.concatStringsSep "\n" (map (entry: "export ${entry.key}=\"${entry.value}\"") pluginEnvAll)}
+      ${lib.concatStringsSep "\n" (map (entry: ''
+        if [ -f "${entry.value}" ]; then
+          export ${entry.key}="$(cat "${entry.value}")"
+        else
+          export ${entry.key}="${entry.value}"
+        fi
+      '') pluginEnvAll)}
 
       exec "${gatewayPackage}/bin/openclaw" "$@"
     '';