Add a unified image budget (#37206)

## What changed

- Add the gated `unified_image_budget` feature for models that support original image detail or Responses Lite.
- Apply one 6,000-pixel, 10,000-patch preprocessing limit regardless of legacy image detail hints.
- Hide detail controls from `view_image` and code mode while continuing to accept existing hints for compatibility.
- Preserve detail-based resizing and tool contracts for unsupported models.

## Testing

- Cover unified resizing limits, Responses Lite, legacy detail hints, unsupported models, and `view_image` integration in code mode.

GitOrigin-RevId: cb07bff1669a96599fdfd076b3d9ec80f2b6fff7

codex-rs/features/src/lib.rs

@@ -224,6 +224,8 @@ pub enum Feature {
     ImageGeneration,
     /// Tell the model when a prompt image was resized and include its dimensions.
     ImageResizeNotice,
+    /// Apply one shared pixel and token budget to every image, regardless of legacy detail hints.
+    UnifiedImageBudget,
     /// Removed compatibility flag for always-on centralized image preparation.
     ResizeAllImages,
     /// Removed compatibility flag for always-on response item IDs.
@@ -1276,6 +1278,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::UnderDevelopment,
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::UnifiedImageBudget,
+        key: "unified_image_budget",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::ResizeAllImages,
         key: "resize_all_images",