[codex] nest sleep config under current time reminder (#29910)

## Summary

- move sleep tool enablement from top-level `[features].sleep_tool` to
`[features.current_time_reminder].sleep_tool`
- remove the standalone `Feature::SleepTool` flag and gate `clock.sleep`
from resolved current-time configuration
- update config schema, config-lock materialization, and existing sleep
coverage

Stacked on #29907.

codex-rs/core/src/tools/spec_plan.rs

@@ -744,10 +744,14 @@ fn add_core_utility_tools(context: &CoreToolPlanContext<'_>, planned_tools: &mut
 
     if features.enabled(Feature::CurrentTimeReminder) {
         planned_tools.add(CurrentTimeHandler);
-    }
-
-    if features.enabled(Feature::SleepTool) {
-        planned_tools.add(SleepHandler);
+        if turn_context
+            .config
+            .current_time_reminder
+            .as_ref()
+            .is_some_and(|config| config.sleep_tool)
+        {
+            planned_tools.add(SleepHandler);
+        }
     }
 
     if tool_suggest_enabled(turn_context)