Remove git commands from dangerous command checks (#11510)

### Motivation

- Git subcommand matching was being classified as "dangerous" and caused
benign developer workflows (for example `git push --force-with-lease`)
to be blocked by the preflight policy.
- The change aligns behavior with the intent to reserve the dangerous
checklist for truly destructive shell ops (e.g. `rm -rf`) and avoid
surprising developer-facing blocks.

### Description

- Remove git-specific subcommand checks from
`is_dangerous_to_call_with_exec` in
`codex-rs/shell-command/src/command_safety/is_dangerous_command.rs`,
leaving only explicit `rm` and `sudo` passthrough checks.
- Deleted the git-specific helper logic that classified `reset`,
`branch`-delete, `push` (force/delete/refspec) and `clean --force` as
dangerous.
- Updated unit tests in the same file to assert that various `git
reset`/`git branch`/`git push`/`git clean` variants are no longer
classified as dangerous.
- Kept `find_git_subcommand` (used by safe-command classification)
intact so safe/unsafe parsing elsewhere remains functional.

### Testing

- Ran formatter with `just fmt` successfully.  
- Ran unit tests with `cargo test -p codex-shell-command` and all tests
passed (`144 passed; 0 failed`).

------
[Codex
Task](https://chatgpt.com/codex/tasks/task_i_698d19dedb4883299c3ceb5bbc6a0dcf)

codex-rs/core/src/exec_policy.rs

@@ -1385,8 +1385,8 @@ prefix_rule(
     }
 
     #[tokio::test]
-    async fn dangerous_git_push_requires_approval_in_danger_full_access() {
-        let command = vec_str(&["git", "push", "origin", "+main"]);
+    async fn dangerous_rm_rf_requires_approval_in_danger_full_access() {
+        let command = vec_str(&["rm", "-rf", "/tmp/nonexistent"]);
         let manager = ExecPolicyManager::default();
         let requirement = manager
             .create_exec_approval_requirement_for_command(ExecApprovalRequest {