feat(hermes): surface providers: dict entries read-only

Hermes v12+ migrated some provider entries from the `custom_providers:`
list into a `providers:` dict (keyed by id). CC Switch previously
ignored that source entirely, leaving users blind to providers they had
configured via Hermes' own Web UI; the only feedback was a generic
migration warning in the health banner.

`get_providers()` now unions both sources, matching upstream
`get_compatible_custom_providers` dedup order (list wins on name
collision). Entries coming from the dict carry a `_cc_source =
"providers_dict"` marker plus the original `provider_key`, which the
UI layer will use to render them read-only. `set_provider` and
`remove_provider` now refuse to touch dict-only entries, steering the
user to Hermes Web UI. `sanitize_hermes_provider_keys` strips the UI
markers on write so they never reach YAML.

The `schema_migrated_v12` health warning copy reframes the situation:
entries are shown read-only in CC Switch rather than invisible.

src/components/hermes/HermesHealthBanner.tsx

@@ -63,7 +63,7 @@ function getWarningText(
     case "schema_migrated_v12":
       return t("hermes.health.schemaMigratedV12", {
         defaultValue:
-          "Hermes' newer schema moved some providers into the 'providers:' dict. CC Switch only manages 'custom_providers:' — edit or remove those entries via Hermes Web UI.",
+          "Hermes' newer schema moved some providers into the 'providers:' dict. They are shown read-only in CC Switch — edit or remove those entries via Hermes Web UI.",
       });
     default:
       return fallback;

src/i18n/locales/en.json

@@ -1685,7 +1685,7 @@
       "modelDefaultNotInProvider": "model.default is not in the selected provider's models list.",
       "duplicateProviderName": "custom_providers contains duplicate provider names — only one entry will be used.",
       "duplicateProviderBaseUrl": "custom_providers contains duplicate base_urls — possible accidental copy.",
-      "schemaMigratedV12": "Hermes' newer schema moved some providers into the 'providers:' dict. CC Switch only manages 'custom_providers:' — edit or remove those entries via Hermes Web UI."
+      "schemaMigratedV12": "Hermes' newer schema moved some providers into the 'providers:' dict. They are shown read-only in CC Switch — edit or remove those entries via Hermes Web UI."
     },
     "memory": {
       "title": "Memory",

src/i18n/locales/ja.json

@@ -1685,7 +1685,7 @@
       "modelDefaultNotInProvider": "model.default は選択中のプロバイダーのモデル一覧に含まれていません。",
       "duplicateProviderName": "custom_providers にプロバイダー名の重複があります。1 件のみ有効になります。",
       "duplicateProviderBaseUrl": "custom_providers に重複した base_url があります。誤ってコピーされた可能性があります。",
-      "schemaMigratedV12": "Hermes の新しいスキーマでは一部のプロバイダーが 'providers:' dict に移動しました。CC Switch は 'custom_providers:' のみを管理します。該当する項目は Hermes Web UI で編集・削除してください。"
+      "schemaMigratedV12": "Hermes の新しいスキーマでは一部のプロバイダーが 'providers:' dict に移動しました。CC Switch では読み取り専用で表示されます。編集・削除は Hermes Web UI から行ってください。"
     },
     "memory": {
       "title": "メモリ",

src/i18n/locales/zh.json

@@ -1685,7 +1685,7 @@
       "modelDefaultNotInProvider": "model.default 指向的模型不在所选供应商的模型列表中。",
       "duplicateProviderName": "custom_providers 中存在重复的供应商名，只会有一条生效。",
       "duplicateProviderBaseUrl": "custom_providers 中存在重复的 base_url，可能是意外复制。",
-      "schemaMigratedV12": "Hermes 新版 schema 把部分供应商移到了 'providers:' dict。CC Switch 只管理 'custom_providers:'，请在 Hermes Web UI 编辑或删除这些条目。"
+      "schemaMigratedV12": "Hermes 新版 schema 把部分供应商移到了 'providers:' dict。CC Switch 中以只读方式显示，编辑或删除请通过 Hermes Web UI 操作。"
     },
     "memory": {
       "title": "记忆管理",