core: resolve view_image paths in selected environment (#29526)

## Why

view_image needs to support foreign OS remote executors.

## What

- resolve image paths against the selected environment as `PathUri` and
read them through that environment's filesystem
- keep app-server's public path field wire-compatible as
`LegacyAppPathString`, with purpose-specific UI rendering
- cover relative and absolute target-native paths in the core
integration test and run the full `view_image` suite under wine-exec
without skips

codex-rs/app-server-protocol/src/protocol/v2/item.rs

@@ -356,7 +356,10 @@ pub enum ThreadItem {
     },
     #[serde(rename_all = "camelCase")]
     #[ts(rename_all = "camelCase")]
-    ImageView { id: String, path: AbsolutePathBuf },
+    ImageView {
+        id: String,
+        path: LegacyAppPathString,
+    },
     #[serde(rename_all = "camelCase")]
     #[ts(rename_all = "camelCase")]
     Sleep {
@@ -855,7 +858,7 @@ impl From<CoreTurnItem> for ThreadItem {
             },
             CoreTurnItem::ImageView(image) => ThreadItem::ImageView {
                 id: image.id,
-                path: image.path,
+                path: image.path.into(),
             },
             CoreTurnItem::Sleep(sleep) => ThreadItem::Sleep {
                 id: sleep.id,

codex-rs/app-server-protocol/src/protocol/v2/tests.rs

@@ -2574,14 +2574,14 @@ fn core_turn_item_into_thread_item_converts_supported_variants() {
 
     let image_view_item = TurnItem::ImageView(ImageViewItem {
         id: "view-image-1".to_string(),
-        path: test_path_buf("/tmp/view-image.png").abs(),
+        path: PathUri::from_abs_path(&test_path_buf("/tmp/view-image.png").abs()),
     });
 
     assert_eq!(
         ThreadItem::from(image_view_item),
         ThreadItem::ImageView {
             id: "view-image-1".to_string(),
-            path: test_path_buf("/tmp/view-image.png").abs(),
+            path: LegacyAppPathString::from_abs_path(&test_path_buf("/tmp/view-image.png").abs()),
         }
     );