feat(policy): map --yolo to allowedTools wildcard policy

This PR maps the `--yolo` flag natively into a wildcard policy array
(`allowedTools: ["*"]`) and removes the concept of `ApprovalMode.YOLO` as a
distinct state in the application, fulfilling issue #11303.

This removes the hardcoded `ApprovalMode.YOLO` state and its associated
UI/bypasses. The `PolicyEngine` now evaluates YOLO purely via data-driven rules.

- Removes `ApprovalMode.YOLO`
- Removes UI toggle (`Ctrl+Y`) and indicators for YOLO
- Removes `yolo.toml`
- Updates A2A server and CLI config logic to translate YOLO into a wildcard tool
- Rewrites policy engine tests to evaluate the wildcard
- Enforces enterprise `disableYoloMode` and `secureModeEnabled` controls
  by actively preventing manual `--allowed-tools=*` bypasses.

Fixes #11303

docs/cli/plan-mode.md

@@ -46,8 +46,9 @@ To start Plan Mode while using Gemini CLI:
   calls the
   [`enter_plan_mode`](../tools/planning.md#1-enter_plan_mode-enterplanmode) tool
   to switch modes.
-  > **Note:** This tool is not available when Gemini CLI is in
-  > [YOLO mode](../reference/configuration.md#command-line-arguments).
+  > **Note:** This tool is not available when Gemini CLI has been instructed to
+  > [auto-approve all actions](../reference/configuration.md#command-line-arguments)
+  > (e.g. via `--yolo`).
 
 ## How to use Plan Mode