Fix misleading 'maximize' high effort description on xhigh models (#7874)

## Notes
- switch misleading High reasoning effort descriptions from "Maximizes
reasoning depth" to "Higher reasoning depth" across models with xhigh
reasoning. Affects GPT-5.1 Codex Max and Robin
- refresh model list fixtures and chatwidget snapshots to match new copy

## Revision
- R2: Change 'Higher' to 'Greater'
- R1: Initial

## Testing

<img width="583" height="142" alt="image"
src="https://github.com/user-attachments/assets/1ddd8971-7841-4cb3-b9ba-91095a7435d2"
/>

<img width="838" height="142" alt="image"
src="https://github.com/user-attachments/assets/79aaedbf-7624-4695-b822-93dea7d6a800"
/>

codex-rs/tui2/src/chatwidget/snapshots/codex_tui2__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. High (current)    Maximizes reasoning depth for complex problems
+› 3. High (current)    Greater reasoning depth for complex problems
   4. Extra high        Extra high reasoning depth for complex problems
 
   Press enter to confirm or esc to go back

codex-rs/tui2/src/chatwidget/snapshots/codex_tui2__chatwidget__tests__model_reasoning_selection_popup_extra_high_warning.snap

@@ -7,7 +7,7 @@ expression: popup
   1. Low                   Fast responses with lighter reasoning
   2. Medium (default)      Balances speed and reasoning depth for everyday
                            tasks
-  3. High                  Maximizes reasoning depth for complex problems
+  3. High                  Greater reasoning depth for complex problems
 › 4. Extra high (current)  Extra high reasoning depth for complex problems
                            ⚠ Extra high reasoning effort can quickly consume
                            Plus plan rate limits.

codex-rs/tui2/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. High (current)    Maximizes reasoning depth for complex problems
+› 3. High (current)    Greater reasoning depth for complex problems
   4. Extra high        Extra high reasoning depth for complex problems
 
   Press enter to confirm or esc to go back

codex-rs/tui2/src/chatwidget/snapshots/codex_tui__chatwidget__tests__model_reasoning_selection_popup_extra_high_warning.snap

@@ -8,7 +8,7 @@ expression: popup
   1. Low                   Fast responses with lighter reasoning
   2. Medium (default)      Balances speed and reasoning depth for everyday
                            tasks
-  3. High                  Maximizes reasoning depth for complex problems
+  3. High                  Greater reasoning depth for complex problems
 › 4. Extra high (current)  Extra high reasoning depth for complex problems
                            ⚠ Extra high reasoning effort can quickly consume
                            Plus plan rate limits.