config: remove legacy profile v1 resolution (#24051)

## Why

[#23883](https://github.com/openai/codex/pull/23883) moved user-facing
`--profile` selection onto profile v2, and
[#23886](https://github.com/openai/codex/pull/23886) removed the old CLI
`config_profile` override path. Core still had a second legacy path:
`profile = "..."` could select `[profiles.*]` values while runtime
config was built. Keeping that resolver alive preserves the old
precedence model and profile-carrying surfaces even though profile
selection now points at `$CODEX_HOME/<name>.config.toml`.

## What

- Reject legacy top-level `profile = "..."` config while loading runtime
config, with an error that points callers at `--profile <name>` and
`<name>.config.toml` in the [core load
path](https://github.com/openai/codex/blob/3d923366eca10a29143623124c6c6e538f058269/codex-rs/core/src/config/mod.rs#L2524-L2531).
- Remove the remaining profile-v1 merge points from runtime config
resolution, including features, permissions, model/provider selection,
web search, Windows sandbox settings, TUI settings, role reloads, and
OSS provider lookup.
- Drop the leftover profile override surface from
[`ConfigOverrides`](https://github.com/openai/codex/blob/3d923366eca10a29143623124c6c6e538f058269/codex-rs/core/src/config/mod.rs#L2118-L2148)
and from the MCP server `codex` tool schema.
- Prune profile-precedence tests that only exercised the removed
resolver and replace them with rejection coverage for the legacy
selector.

## Testing

- Not run in this metadata pass.
- Added
[`legacy_profile_selection_is_rejected`](https://github.com/openai/codex/blob/3d923366eca10a29143623124c6c6e538f058269/codex-rs/core/src/config/config_tests.rs#L7942-L7965)
coverage for the new runtime guard.

codex-rs/core/src/windows_sandbox_tests.rs

@@ -78,29 +78,6 @@ fn legacy_mode_supports_alias_key() {
     );
 }
 
-#[test]
-fn resolve_windows_sandbox_mode_prefers_profile_windows() {
-    let cfg = ConfigToml {
-        windows: Some(WindowsToml {
-            sandbox: Some(WindowsSandboxModeToml::Unelevated),
-            ..Default::default()
-        }),
-        ..Default::default()
-    };
-    let profile = ConfigProfile {
-        windows: Some(WindowsToml {
-            sandbox: Some(WindowsSandboxModeToml::Elevated),
-            ..Default::default()
-        }),
-        ..Default::default()
-    };
-
-    assert_eq!(
-        resolve_windows_sandbox_mode(&cfg, &profile),
-        Some(WindowsSandboxModeToml::Elevated)
-    );
-}
-
 #[test]
 fn resolve_windows_sandbox_mode_falls_back_to_legacy_keys() {
     let mut entries = BTreeMap::new();
@@ -114,61 +91,15 @@ fn resolve_windows_sandbox_mode_falls_back_to_legacy_keys() {
     };
 
     assert_eq!(
-        resolve_windows_sandbox_mode(&cfg, &ConfigProfile::default()),
+        resolve_windows_sandbox_mode(&cfg),
         Some(WindowsSandboxModeToml::Unelevated)
     );
 }
 
-#[test]
-fn resolve_windows_sandbox_mode_profile_legacy_false_blocks_top_level_legacy_true() {
-    let mut profile_entries = BTreeMap::new();
-    profile_entries.insert(
-        "experimental_windows_sandbox".to_string(),
-        /*value*/ false,
-    );
-    let profile = ConfigProfile {
-        features: Some(FeaturesToml::from(profile_entries)),
-        ..Default::default()
-    };
-
-    let mut cfg_entries = BTreeMap::new();
-    cfg_entries.insert(
-        "experimental_windows_sandbox".to_string(),
-        /*value*/ true,
-    );
-    let cfg = ConfigToml {
-        features: Some(FeaturesToml::from(cfg_entries)),
-        ..Default::default()
-    };
-
-    assert_eq!(resolve_windows_sandbox_mode(&cfg, &profile), None);
-}
-
-#[test]
-fn resolve_windows_sandbox_private_desktop_prefers_profile_windows() {
-    let cfg = ConfigToml {
-        windows: Some(WindowsToml {
-            sandbox: Some(WindowsSandboxModeToml::Unelevated),
-            sandbox_private_desktop: Some(false),
-        }),
-        ..Default::default()
-    };
-    let profile = ConfigProfile {
-        windows: Some(WindowsToml {
-            sandbox: Some(WindowsSandboxModeToml::Elevated),
-            sandbox_private_desktop: Some(true),
-        }),
-        ..Default::default()
-    };
-
-    assert!(resolve_windows_sandbox_private_desktop(&cfg, &profile));
-}
-
 #[test]
 fn resolve_windows_sandbox_private_desktop_defaults_to_true() {
     assert!(resolve_windows_sandbox_private_desktop(
-        &ConfigToml::default(),
-        &ConfigProfile::default()
+        &ConfigToml::default()
     ));
 }
 
@@ -182,8 +113,5 @@ fn resolve_windows_sandbox_private_desktop_respects_explicit_cfg_value() {
         ..Default::default()
     };
 
-    assert!(!resolve_windows_sandbox_private_desktop(
-        &cfg,
-        &ConfigProfile::default()
-    ));
+    assert!(!resolve_windows_sandbox_private_desktop(&cfg));
 }