fix: use authenticated API for remote config polling (#8266)

## Summary
- Fixes remote config polling to use authenticated API
- Consolidates `loadRemoteConfig` into `refreshRemoteConfig` with auth
control
- Adds unit tests for both auth modes

## Problem
The cloud extension's polling interval was using unauthenticated
`fetch`, causing it to receive only default feature flags instead of
user-specific configurations.

**Root cause:**
1. Bootstrap called `loadRemoteConfig()` (raw `fetch`, no auth) -
correct, auth not initialized yet
2. Extension watch called `refreshRemoteConfig()` (`api.fetchApi`, with
auth) - correct
3. Extension interval called `loadRemoteConfig()` (raw `fetch`, no auth)
- **bug**

## Solution
- Consolidate into single `refreshRemoteConfig()` with optional
`useAuth` parameter (defaults to `true`)
- Bootstrap: `refreshRemoteConfig({ useAuth: false })`
- Polling: `refreshRemoteConfig()` (authenticated by default)

## Test Plan
- Unit tests verify both auth modes
- `pnpm typecheck`, `pnpm lint`, `pnpm test:unit` all pass

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8266-fix-use-authenticated-API-for-remote-config-polling-2f16d73d3650817ea7b0e3a7e3ccf12a)
by [Unito](https://www.unito.io)

src/platform/remoteConfig/remoteConfig.ts

@@ -8,7 +8,6 @@
  * - Avoiding vendor lock-in for native apps
  *
  * This module is tree-shaken in OSS builds.
- * Used for initial config load in main.ts and polling in the extension.
  */
 
 import { ref } from 'vue'
@@ -29,26 +28,3 @@ export function configValueOrDefault<K extends keyof RemoteConfig>(
   const configValue = remoteConfig[key]
   return configValue || defaultValue
 }
-
-/**
- * Loads remote configuration from the backend /api/features endpoint
- * and updates the reactive remoteConfig ref
- */
-export async function loadRemoteConfig(): Promise<void> {
-  try {
-    const response = await fetch('/api/features', { cache: 'no-store' })
-    if (response.ok) {
-      const config = await response.json()
-      window.__CONFIG__ = config
-      remoteConfig.value = config
-    } else {
-      console.warn('Failed to load remote config:', response.statusText)
-      window.__CONFIG__ = {}
-      remoteConfig.value = {}
-    }
-  } catch (error) {
-    console.error('Failed to fetch remote config:', error)
-    window.__CONFIG__ = {}
-    remoteConfig.value = {}
-  }
-}