[codex] Treat max as a first-class reasoning effort (#30467)

## Why

The Bedrock GPT-5.6 catalog advertises `max`, but Codex treated it as an
opaque custom effort. That made the reasoning picker render it as
lowercase `max` while known efforts use productized labels.

Making `max` a known effort aligns catalog data, parsing, and UI
presentation without changing the `max` wire value or persisted
representation.

## What changed

- Add first-class `ReasoningEffort::Max` parsing and serialization.
- Use the typed effort in the Bedrock catalog and render it as `Max` in
the TUI.
- Preserve forward-compatible custom-effort coverage with a genuinely
unknown `future` value.

### Before
<img width="559" height="124" alt="Screenshot 2026-06-28 at 12 08 47 PM"
src="https://github.com/user-attachments/assets/7c43cf4f-020b-4605-9239-0a9c97eb7364"
/>

### After
<img width="558" height="107" alt="Screenshot 2026-06-28 at 12 09 10 PM"
src="https://github.com/user-attachments/assets/b9cc5ded-c940-43b4-b024-bba25abe0a17"
/>

codex-rs/tui/src/chatwidget/model_popups.rs

@@ -505,6 +505,7 @@ impl ChatWidget {
             ReasoningEffortConfig::Medium => "Medium".to_string(),
             ReasoningEffortConfig::High => "High".to_string(),
             ReasoningEffortConfig::XHigh => "Extra high".to_string(),
+            ReasoningEffortConfig::Max => "Max".to_string(),
             ReasoningEffortConfig::Ultra => "Ultra".to_string(),
             ReasoningEffortConfig::Custom(value) => value.clone(),
         }

codex-rs/tui/src/chatwidget/reasoning_shortcuts.rs

@@ -225,7 +225,7 @@ mod tests {
 
     #[test]
     fn next_reasoning_effort_uses_advertised_order_for_custom_levels() {
-        let custom_effort = ReasoningEffortConfig::Custom("max".to_string());
+        let custom_effort = ReasoningEffortConfig::Custom("future".to_string());
         let choices = vec![
             ReasoningEffortConfig::High,
             ReasoningEffortConfig::Low,

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__model_reasoning_selection_popup.snap

@@ -6,7 +6,7 @@ expression: popup
 
   1. Low               Fast responses with lighter reasoning
   2. Medium (default)  Balances speed and reasoning depth for everyday tasks
-  3. max               Maximum available reasoning
+  3. Max               Maximum available reasoning
 › 4. High (current)    Greater reasoning depth for complex problems
   5. Extra high        Extra high reasoning depth for complex problems
 

codex-rs/tui/src/chatwidget/tests/popups_and_settings.rs

@@ -3191,7 +3191,7 @@ async fn model_reasoning_selection_popup_snapshot() {
     preset.supported_reasoning_efforts.insert(
         2,
         ReasoningEffortPreset {
-            effort: ReasoningEffortConfig::Custom("max".to_string()),
+            effort: ReasoningEffortConfig::Max,
             description: "Maximum available reasoning".to_string(),
         },
     );
@@ -3204,7 +3204,7 @@ async fn model_reasoning_selection_popup_snapshot() {
 #[tokio::test]
 async fn model_reasoning_selection_popup_applies_custom_effort() {
     let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.4")).await;
-    let custom_effort = ReasoningEffortConfig::Custom("max".to_string());
+    let custom_effort = ReasoningEffortConfig::Custom("future".to_string());
     chat.set_reasoning_effort(Some(ReasoningEffortConfig::XHigh));
 
     let mut preset = get_available_model(&chat, "gpt-5.4");