diffs: add configurable viewer base URL (#59341)

Merged via squash.

Prepared head SHA: 3c2a84849f
Co-authored-by: gumadeiras <5599352+gumadeiras@users.noreply.github.com>
Co-authored-by: gumadeiras <5599352+gumadeiras@users.noreply.github.com>
Reviewed-by: @gumadeiras

extensions/diffs/openclaw.plugin.json

@@ -4,6 +4,10 @@
   "description": "Read-only diff viewer and file renderer for agents.",
   "skills": ["./skills"],
   "uiHints": {
+    "viewerBaseUrl": {
+      "label": "Viewer Base URL",
+      "help": "Persistent gateway base URL used for returned viewer links when a tool call does not pass baseUrl."
+    },
     "defaults.fontFamily": {
       "label": "Default Font",
       "help": "Preferred font family name for diff content and headers."
@@ -69,6 +73,9 @@
     "type": "object",
     "additionalProperties": false,
     "properties": {
+      "viewerBaseUrl": {
+        "type": "string"
+      },
       "defaults": {
         "type": "object",
         "additionalProperties": false,