Preserve image detail in app-server inputs (#20693)

## Summary

- Add optional image detail to user image inputs across core, app-server
v2, thread history/event mapping, and the generated app-server
schemas/types.
- Preserve requested detail when serializing Responses image inputs:
omitted detail stays on the existing `high` default, while explicit
`original` keeps local images on the original-resolution path.
- Support `high`/`original` consistently for tool image outputs,
including MCP `codex/imageDetail`, code-mode image helpers, and
`view_image`.

codex-rs/app-server-protocol/schema/json/v2/ThreadListResponse.json

@@ -448,6 +448,13 @@
       ],
       "type": "object"
     },
+    "ImageDetail": {
+      "enum": [
+        "high",
+        "original"
+      ],
+      "type": "string"
+    },
     "McpToolCallError": {
       "properties": {
         "message": {
@@ -1827,6 +1834,17 @@
         },
         {
           "properties": {
+            "detail": {
+              "anyOf": [
+                {
+                  "$ref": "#/definitions/ImageDetail"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "default": null
+            },
             "type": {
               "enum": [
                 "image"
@@ -1847,6 +1865,17 @@
         },
         {
           "properties": {
+            "detail": {
+              "anyOf": [
+                {
+                  "$ref": "#/definitions/ImageDetail"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "default": null
+            },
             "path": {
               "type": "string"
             },