refactor(codex): unify custom model_provider routing key to "custom"

- Always emit `model_provider = "custom"` from deep link, UniversalProvider, and the universal form modal so future writes share one stable routing key.
- Add `codex_provider_template_v1` local migration that rewrites legacy keys (aihubmix/ccswitch/...) under `[model_providers.custom]`, updates profile refs, and backs up the original settings_config under `~/.cc-switch/backups/<timestamp>/providers/`.
- Tighten history migration source detection to a whitelist plus `[model_providers.<id>]` existence check so user-authored keys are never rewritten in jsonl/state DB.
- Encode deep link name/model/endpoint through `toml_edit::Value` so display names containing quotes or backslashes no longer break the generated config.toml.
- Stabilize provider settings backup filename hash with Sha256 (was process-random SipHash).

src-tauri/src/settings.rs

@@ -178,13 +178,15 @@ impl WebDavSyncSettings {
 
 /// 本机自动迁移状态。
 ///
-/// 这里记录的是设备级操作（例如修改本机 `~/.codex` 文件），不随数据库同步。
+/// 这里记录的是本机启动时执行过的一次性迁移；标记不随数据库同步。
 #[derive(Debug, Clone, Serialize, Deserialize, Default)]
 #[serde(rename_all = "camelCase")]
 pub struct LocalMigrations {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub codex_third_party_history_provider_bucket_v1:
         Option<CodexThirdPartyHistoryProviderBucketMigration>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub codex_provider_template_v1: Option<CodexProviderTemplateMigration>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -202,6 +204,14 @@ pub struct CodexThirdPartyHistoryProviderBucketMigration {
     pub scanned_history_files: bool,
 }
 
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct CodexProviderTemplateMigration {
+    pub completed_at: String,
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub migrated_provider_ids: Vec<String>,
+}
+
 /// 应用设置结构
 ///
 /// 存储设备级别设置，保存在本地 `~/.cc-switch/settings.json`，不随数据库同步。
@@ -610,6 +620,25 @@ pub fn mark_codex_third_party_history_provider_bucket_migrated(
     })
 }
 
+pub fn is_codex_provider_template_migrated() -> bool {
+    get_settings()
+        .local_migrations
+        .as_ref()
+        .and_then(|migrations| migrations.codex_provider_template_v1.as_ref())
+        .is_some()
+}
+
+pub fn mark_codex_provider_template_migrated(
+    migration: CodexProviderTemplateMigration,
+) -> Result<(), AppError> {
+    mutate_settings(|settings| {
+        let migrations = settings
+            .local_migrations
+            .get_or_insert_with(Default::default);
+        migrations.codex_provider_template_v1 = Some(migration);
+    })
+}
+
 /// 从文件重新加载设置到内存缓存
 /// 用于导入配置等场景，确保内存缓存与文件同步
 pub fn reload_settings() -> Result<(), AppError> {