feat: add user secrets management panel (#8473)

## Summary

Add a Secrets panel to user settings for managing third-party API keys
(HuggingFace, Civitai). Secrets are encrypted server-side; plaintext
values are never returned.

## Changes

- Add `SecretsPanel` to settings for managing third-party API keys
- Create `secretsApi` service following the `workspaceApi` pattern
- Add `SecretListItem` and `SecretFormDialog` components
- Add `user_secrets_enabled` feature flag
- Support HuggingFace and Civitai providers
- Add i18n translations for secrets UI

## Files Added

- `src/platform/secrets/types.ts` - TypeScript types
- `src/platform/secrets/api/secretsApi.ts` - Axios-based API service
- `src/platform/secrets/components/SecretsPanel.vue` - Main settings
panel
- `src/platform/secrets/components/SecretListItem.vue` - Individual
secret row
- `src/platform/secrets/components/SecretFormDialog.vue` - Create/edit
dialog

## Files Modified

- `src/platform/remoteConfig/types.ts` - Add `user_secrets_enabled` flag
type
- `src/composables/useFeatureFlags.ts` - Add flag getter
- `src/platform/settings/composables/useSettingUI.ts` - Integrate
secrets panel
- `src/locales/en/main.json` - Add translations

## Testing

Panel appears in Settings under:
- "Workspace" group when team workspaces is enabled
- "Account" group in legacy mode

Only visible when user is logged in AND `user_secrets_enabled` feature
flag is enabled.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8473-feat-add-user-secrets-management-panel-2f86d73d36508187b4a1ed04ce07ce51)
by [Unito](https://www.unito.io)


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Secrets management UI in Settings with create/edit/delete for API
keys/secrets; settings dialog entry and contextual Secrets hint in
upload/import flows (feature-flag gated).
* **APIs**
* Added backend-facing secrets CRUD surface and client-side
form/composable support for managing secrets.
* **Localization**
* New English translations for Secrets UI and many expanded asset
import/upload error and hint messages.
* **Tests**
* Comprehensive unit tests for secrets UI, form flows, and composables.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Amp <amp@ampcode.com>

src/platform/settings/components/SettingDialogContent.vue

@@ -129,6 +129,7 @@ const { defaultPanel } = defineProps<{
     | 'credits'
     | 'subscription'
     | 'workspace'
+    | 'secrets'
 }>()
 
 const { flags } = useFeatureFlags()

src/platform/settings/composables/useSettingUI.ts

@@ -30,6 +30,7 @@ export function useSettingUI(
     | 'credits'
     | 'subscription'
     | 'workspace'
+    | 'secrets'
 ) {
   const { t } = useI18n()
   const { isLoggedIn } = useCurrentUser()
@@ -169,6 +170,21 @@ export function useSettingUI(
     () => teamWorkspacesEnabled.value && isLoggedIn.value
   )
 
+  const secretsPanel: SettingPanelItem = {
+    node: {
+      key: 'secrets',
+      label: 'Secrets',
+      children: []
+    },
+    component: defineAsyncComponent(
+      () => import('@/platform/secrets/components/SecretsPanel.vue')
+    )
+  }
+
+  const shouldShowSecretsPanel = computed(
+    () => flags.userSecretsEnabled && isLoggedIn.value
+  )
+
   const keybindingPanel: SettingPanelItem = {
     node: {
       key: 'keybinding',
@@ -213,7 +229,8 @@ export function useSettingUI(
       ...(isElectron() ? [serverConfigPanel] : []),
       ...(shouldShowPlanCreditsPanel.value && subscriptionPanel
         ? [subscriptionPanel]
-        : [])
+        : []),
+      ...(shouldShowSecretsPanel.value ? [secretsPanel] : [])
     ].filter((panel) => panel !== null && panel.component)
   )
 
@@ -249,7 +266,8 @@ export function useSettingUI(
         ...(isLoggedIn.value &&
         !(isCloud && window.__CONFIG__?.subscription_required)
           ? [creditsPanel.node]
-          : [])
+          : []),
+        ...(shouldShowSecretsPanel.value ? [secretsPanel.node] : [])
       ].map(translateCategory)
     }),
     // General settings - Profile + all core settings + special panels
@@ -290,6 +308,7 @@ export function useSettingUI(
         subscriptionPanel
           ? [subscriptionPanel.node]
           : []),
+        ...(shouldShowSecretsPanel.value ? [secretsPanel.node] : []),
         ...(isLoggedIn.value &&
         !(isCloud && window.__CONFIG__?.subscription_required)
           ? [creditsPanel.node]