fix(provider): exclude injected artifacts and routing fields from Codex common-config extraction

extract_codex_common_config kept several fields in the shared snippet
that must never cross providers:

- [mcp_servers] and the legacy [mcp.servers] form: owned by the DB
  mcp_servers table; once in the snippet they get merged into every
  opted-in provider and no sync path can ever clean them up.
- top-level experimental_bearer_token: normally lives inside
  [model_providers.<id>] (stripped with the whole table), but three
  fallbacks write it at top level -- leaking the API key into the
  shared snippet.
- model_catalog_json: per-provider catalog projection pointer.
- web_search, only when it equals the injected "disabled" sentinel;
  a user-set value remains a shareable preference.
- top-level wire_api: same provider-routing semantics as top-level
  base_url (the fallback target when no model_provider is set); leaking
  it would rewrite the next provider's protocol selection.

This makes the extractor safe as the source for switch-time
common-config autosync.

src-tauri/src/codex_config.rs

@@ -15,14 +15,14 @@ pub const CC_SWITCH_CODEX_MODEL_PROVIDER_ID: &str = "custom";
 pub const CC_SWITCH_CODEX_MODEL_CATALOG_FILENAME: &str = "cc-switch-model-catalog.json";
 
 /// Top-level `config.toml` key that controls Codex's built-in web-search tool.
-const CODEX_WEB_SEARCH_FIELD: &str = "web_search";
+pub(crate) const CODEX_WEB_SEARCH_FIELD: &str = "web_search";
 /// Value that disables the web-search tool. Some native `/responses` gateways
 /// reject a `web_search` tool with `responses_feature_not_supported` ("tool type
 /// 'web_search' is not supported by this gateway phase"), so for those we write
 /// this per the vendors' official Codex docs. Also doubles as cc-switch's
 /// ownership sentinel: we only ever remove a `web_search` key whose value equals
 /// this string, never a user's own setting.
-const CODEX_WEB_SEARCH_DISABLED: &str = "disabled";
+pub(crate) const CODEX_WEB_SEARCH_DISABLED: &str = "disabled";
 
 /// Native `/responses` gateways whose first-party models do NOT support the Codex
 /// `web_search` hosted tool. A BLACKLIST (default-on): everything not listed keeps