chore(core) move model_instructions_template config (#9871)

## Summary
Move `model_instructions_template` config to the experimental slug while
we iterate on this feature

## Testing
- [x] Tested locally, unit tests still pass

codex-rs/core/src/models_manager/model_info.rs

@@ -169,6 +169,16 @@ pub(crate) fn find_model_info_for_slug(slug: &str) -> ModelInfo {
         model_info!(
             slug,
             base_instructions: GPT_5_2_CODEX_INSTRUCTIONS.to_string(),
+            model_instructions_template: Some(ModelInstructionsTemplate {
+                template: GPT_5_2_CODEX_INSTRUCTIONS_TEMPLATE.to_string(),
+                personality_messages: Some(PersonalityMessages(BTreeMap::from([(
+                    Personality::Friendly,
+                    PERSONALITY_FRIENDLY.to_string(),
+                ), (
+                    Personality::Pragmatic,
+                    PERSONALITY_PRAGMATIC.to_string(),
+                )]))),
+            }),
             apply_patch_tool_type: Some(ApplyPatchToolType::Freeform),
             shell_type: ConfigShellToolType::ShellCommand,
             supports_parallel_tool_calls: true,
@@ -203,16 +213,6 @@ pub(crate) fn find_model_info_for_slug(slug: &str) -> ModelInfo {
             truncation_policy: TruncationPolicyConfig::tokens(10_000),
             context_window: Some(CONTEXT_WINDOW_272K),
             supported_reasoning_levels: supported_reasoning_level_low_medium_high_xhigh(),
-            model_instructions_template: Some(ModelInstructionsTemplate {
-                template: GPT_5_2_CODEX_INSTRUCTIONS_TEMPLATE.to_string(),
-                personality_messages: Some(PersonalityMessages(BTreeMap::from([(
-                    Personality::Friendly,
-                    PERSONALITY_FRIENDLY.to_string(),
-                ), (
-                    Personality::Pragmatic,
-                    PERSONALITY_PRAGMATIC.to_string(),
-                )]))),
-            }),
         )
     } else if slug.starts_with("gpt-5.1-codex-max") {
         model_info!(