core: expose permission profile picker metadata (#22928)

## Why

The `/permissions` picker needs a config-level way to distinguish legacy
anonymous presets from named permission-profile mode. That signal cannot
be inferred reliably in the TUI, especially for the edge case where
`default_permissions = ":workspace"` is present without a
`[permissions]` table.

## What changed

- Expose whether the merged config is explicitly in permission-profile
mode.
- Expose the configured custom permission profile IDs alongside the
built-in profile semantics.
- Add regression coverage for profile mode detection and custom profile
metadata, including the `default_permissions = ":workspace"` case.
- Update the thread-manager sample config literal to match the expanded
config shape.

## Stack

1. **This PR**: config metadata needed by downstream permission-profile
consumers.
2. [#22931](https://github.com/openai/codex/pull/22931): refresh active
permission profiles through runtime/session/network state.
3. [#21559](https://github.com/openai/codex/pull/21559): switch
`/permissions` to the profile-aware TUI picker.

## Verification

- `cargo check -p codex-thread-manager-sample`
- `cargo test -p codex-core
default_permissions_can_select_builtin_profile_without_permissions_table`
- `cargo test -p codex-core
permissions_profiles_allow_direct_write_roots_outside_workspace_root`

codex-rs/thread-manager-sample/src/main.rs

@@ -175,6 +175,8 @@ fn new_config(model: Option<String>, arg0_paths: Arg0DispatchPaths) -> anyhow::R
             Constrained::allow_any(AskForApproval::Never),
             Constrained::allow_any(PermissionProfile::read_only()),
         )?,
+        explicit_permission_profile_mode: false,
+        custom_permission_profile_ids: Vec::new(),
         approvals_reviewer: ApprovalsReviewer::User,
         enforce_residency: Constrained::allow_any(/*initial_value*/ None),
         hide_agent_reasoning: false,