Add audio file references with explicit runtime rejection (#58430)

## What changed

- Allow audio inputs to carry uploaded file references via `fileId` in the app-server API and `file_id` in model content, preserving existing inline audio shapes and Python class names.
- Preserve mixed inline and file-backed audio ordering through history reconstruction and migration, and budget file-backed audio conservatively when duration is unknown.
- Keep uploaded audio disabled at runtime: reject it before inference or raw history injection, preserve accompanying text, and prevent rejected attachments from reaching follow-up or resumed requests.

## Testing

Add coverage for wire-format round trips, SDK compatibility, mixed audio history ordering, and rejection during turn start, steering, task completion, and raw injection.

GitOrigin-RevId: 70895c47a2494c0c9936348ad1250eb1b7b892a6

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

@@ -2731,6 +2731,32 @@
           "type": "object"
         },
         {
+          "anyOf": [
+            {
+              "properties": {
+                "url": {
+                  "type": "string"
+                }
+              },
+              "required": [
+                "url"
+              ],
+              "title": "UrlUserInput",
+              "type": "object"
+            },
+            {
+              "properties": {
+                "fileId": {
+                  "type": "string"
+                }
+              },
+              "required": [
+                "fileId"
+              ],
+              "title": "FileIdUserInput",
+              "type": "object"
+            }
+          ],
           "properties": {
             "type": {
               "enum": [
@@ -2738,14 +2764,10 @@
               ],
               "title": "AudioUserInputType",
               "type": "string"
-            },
-            "url": {
-              "type": "string"
             }
           },
           "required": [
-            "type",
-            "url"
+            "type"
           ],
           "title": "AudioUserInput",
           "type": "object"