feat(core): enhance shell command validation and add core tools allowlist (#25720)

Co-authored-by: David Pierce <davidapierce@google.com>
Co-authored-by: Keith Schaab <keithsc@google.com>
Co-authored-by: Keith Schaab <keith.schaab@gmail.com>
Co-authored-by: Emily Hedlund <ehedlund@google.com>

docs/reference/configuration.md

@@ -1437,6 +1437,12 @@ their corresponding top-level category object in your `settings.json` file.
   - **Default:** `undefined`
   - **Requires restart:** Yes
 
+- **`tools.confirmationRequired`** (array):
+  - **Description:** Tool names that always require user confirmation. Takes
+    precedence over allowed tools and core tool allowlists.
+  - **Default:** `undefined`
+  - **Requires restart:** Yes
+
 - **`tools.exclude`** (array):
   - **Description:** Tool names to exclude from discovery.
   - **Default:** `undefined`