feat: introduce Permissions (#11633)

## Why
We currently carry multiple permission-related concepts directly on
`Config` for shell/unified-exec behavior (`approval_policy`,
`sandbox_policy`, `network`, `shell_environment_policy`,
`windows_sandbox_mode`).

Consolidating these into one in-memory struct makes permission handling
easier to reason about and sets up the next step: supporting named
permission profiles (`[permissions.PROFILE_NAME]`) without changing
behavior now.

This change is mostly mechanical: it updates existing callsites to go
through `config.permissions`, but it does not yet refactor those
callsites to take a single `Permissions` value in places where multiple
permission fields are still threaded separately.

This PR intentionally **does not** change the on-disk `config.toml`
format yet and keeps compatibility with legacy config keys.

## What Changed
- Introduced `Permissions` in `core/src/config/mod.rs`.
- Added `Config::permissions` and moved effective runtime permission
fields under it:
  - `approval_policy`
  - `sandbox_policy`
  - `network`
  - `shell_environment_policy`
  - `windows_sandbox_mode`
- Updated config loading/building so these effective values are still
derived from the same existing config inputs and constraints.
- Updated Windows sandbox helpers/resolution to read/write via
`permissions`.
- Threaded the new field through all permission consumers across core
runtime, app-server, CLI/exec, TUI, and sandbox summary code.
- Updated affected tests to reference `config.permissions.*`.
- Renamed the struct/field from
`EffectivePermissions`/`effective_permissions` to
`Permissions`/`permissions` and aligned variable naming accordingly.

## Verification
- `just fix -p codex-core -p codex-tui -p codex-cli -p codex-app-server
-p codex-exec -p codex-utils-sandbox-summary`
- `cargo build -p codex-core -p codex-tui -p codex-cli -p
codex-app-server -p codex-exec -p codex-utils-sandbox-summary`

codex-rs/tui/src/lib.rs

@@ -290,7 +290,9 @@ pub async fn run_main(
     .await;
     set_default_client_residency_requirement(config.enforce_residency.value());
 
-    if let Some(warning) = add_dir_warning_message(&cli.add_dir, config.sandbox_policy.get()) {
+    if let Some(warning) =
+        add_dir_warning_message(&cli.add_dir, config.permissions.sandbox_policy.get())
+    {
         #[allow(clippy::print_stderr)]
         {
             eprintln!("Error adding directories: {warning}");
@@ -1004,8 +1006,8 @@ mod tests {
         TurnContextItem {
             turn_id: None,
             cwd,
-            approval_policy: config.approval_policy.value(),
-            sandbox_policy: config.sandbox_policy.get().clone(),
+            approval_policy: config.permissions.approval_policy.value(),
+            sandbox_policy: config.permissions.sandbox_policy.get().clone(),
             model,
             personality: None,
             collaboration_mode: None,
@@ -1123,7 +1125,7 @@ trust_level = "untrusted"
             .build()
             .await?;
         assert_eq!(
-            trusted_config.approval_policy.value(),
+            trusted_config.permissions.approval_policy.value(),
             AskForApproval::OnRequest
         );
 
@@ -1137,7 +1139,7 @@ trust_level = "untrusted"
             .build()
             .await?;
         assert_eq!(
-            untrusted_config.approval_policy.value(),
+            untrusted_config.permissions.approval_policy.value(),
             AskForApproval::UnlessTrusted
         );
         Ok(())