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/protocol/src/protocol.rs

@@ -3399,8 +3399,11 @@ pub struct ExecCommandEndEvent {
 pub struct ViewImageToolCallEvent {
     /// Identifier for the originating tool call.
     pub call_id: String,
-    /// Local filesystem path provided to the tool.
-    pub path: AbsolutePathBuf,
+    /// Filesystem path resolved for the selected environment.
+    ///
+    /// This core event is not exposed directly in the app-server API. App-server
+    /// converts the path to `LegacyAppPathString` when building its public item.
+    pub path: PathUri,
 }
 
 #[derive(Debug, Clone, Deserialize, Serialize, PartialEq, JsonSchema, TS)]