Align Guardian reviews with session configuration (#32747)

## What changed

- Include permission instructions in Guardian review requests and let the review model use its configured tool mode and standard tool plan instead of a Guardian-specific direct-tool override.
- Refine the Guardian policy for tenant policy precedence, authorization scoring, prompt-injection handling, read-only investigation, and post-denial user approval.
- Simplify low-risk allow responses to `{"outcome":"allow"}` regardless of authorization scoring.

## Testing

- Update Guardian request-layout snapshots to cover the permission instructions included in initial and follow-up reviews.

GitOrigin-RevId: eb83571ef61f7b4e854c12e13e7163c6fab43f00

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

@@ -62,10 +62,6 @@ pub(crate) fn tool_user_shell_type(
 }
 
 fn effective_tool_mode(turn_context: &TurnContext) -> ToolMode {
-    if crate::guardian::is_guardian_reviewer_source(&turn_context.session_source) {
-        return ToolMode::Direct;
-    }
-
     turn_context.model_info.tool_mode.unwrap_or_else(|| {
         if turn_context.config.features.enabled(Feature::CodeModeOnly) {
             ToolMode::CodeModeOnly