Auto-approve DangerFullAccess patches on non-sandboxed platforms (#2988)

**What?**
Auto-approve patches when `SandboxPolicy::DangerFullAccess` is enabled
on platforms without sandbox support.
Changes in `codex-rs/core/src/safety.rs`: return
`SafetyCheck::AutoApprove { sandbox_type: SandboxType::None }` when no
sandbox is available and DangerFullAccess is set.

**Why?**
On platforms lacking sandbox support, requiring explicit user approval
despite `DangerFullAccess` being explicitly enabled adds friction
without additional safety. This aligns behavior with the stated policy
intent.

**How?**
Extend `assess_patch_safety` match:

* If `get_platform_sandbox()` returns `Some`, keep `AutoApprove {
sandbox_type }`.
* If `None` **and** `SandboxPolicy::DangerFullAccess`, return
`AutoApprove { SandboxType::None }`.
* Otherwise, fall back to `AskUser`.

**Tests**

* Local checks:
  ```bash
cargo test && cargo clippy --tests && cargo fmt -- --config
imports_granularity=Item
  ```
(Additionally: `just fmt`, `just fix -p codex-core`, `cargo check -p
codex-core`.)

**Docs**
No user-facing CLI changes. No README/help updates needed.

**Risk/Impact**
Reduces prompts on non-sandboxed platforms when DangerFullAccess is
explicitly chosen; consistent with policy semantics.

---------

Co-authored-by: Michael Bolin <bolinfest@gmail.com>

codex-rs/core/src/safety.rs

@@ -53,6 +53,13 @@ pub fn assess_patch_safety(
         // paths outside the project.
         match get_platform_sandbox() {
             Some(sandbox_type) => SafetyCheck::AutoApprove { sandbox_type },
+            None if sandbox_policy == &SandboxPolicy::DangerFullAccess => {
+                // If the user has explicitly requested DangerFullAccess, then
+                // we can auto-approve even without a sandbox.
+                SafetyCheck::AutoApprove {
+                    sandbox_type: SandboxType::None,
+                }
+            }
             None => SafetyCheck::AskUser,
         }
     } else if policy == AskForApproval::Never {