change cloud feature flags to be loaded dynamically at runtime rather than set in build (#6246)

## Summary

Implements server-side remote configuration to decouple runtime behavior
from build artifacts, enabling dynamic configuration updates without
redeployment.

## Technical Changes

- **Replaced** build-time constants (`__MIXPANEL_TOKEN__`,
`__BUILD_FLAGS__`) with runtime configuration loaded from
`/api/features`
- Configuration now sourced from `window.__CONFIG__` (hydrated from
`/api/features` endpoint)
- **Added** `src/platform/remoteConfig/` service that polls server
configuration every 30 seconds
- **Modified** application bootstrap sequence in `main.ts` to load
remote config before module initialization (required for cloud builds)
- **Removed** global constants: `__BUILD_FLAGS__`, `__MIXPANEL_TOKEN__`.
Runtime subscription enforcement toggle via `subscription_required` flag
- Server health alerts with variant-based severity rendering
(info/warning/error) via topbar badges

## Rationale

- **Build-once-deploy-anywhere**: Single immutable artifact promoted
through environments (staging → production)
- **Zero-downtime configuration**: Update behavior without rebuilding or
redeploying the application
- **Incident response**: Disable features or display alerts dynamically
in response to outages or degraded service
- **Instant rollback**: Revert configuration changes server-side without
artifact redeployment
- **Progressive delivery**: Enable A/B testing, canary releases, and
user/region-based configuration
- **Environment parity**: Eliminate configuration drift between staging
and production builds
- Decouples deployment cadence from configuration changes
- Enables GitOps workflows for configuration management separate from
code deployments
- Supports real-time operational control of client behavior
- Reduces build matrix complexity (no per-environment builds)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6246-change-cloud-feature-flags-to-be-loaded-dynamically-at-runtime-rather-than-set-in-build-2966d73d3650811cbb41c9093961037a)
by [Unito](https://www.unito.io)

src/platform/remoteConfig/remoteConfig.ts

@@ -0,0 +1,45 @@
+/**
+ * Remote configuration service
+ *
+ * Fetches configuration from the server at runtime, enabling:
+ * - Feature flags without rebuilding
+ * - Server-side feature discovery
+ * - Version compatibility management
+ * - 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'
+
+import type { RemoteConfig } from './types'
+
+/**
+ * Reactive remote configuration
+ * Updated whenever config is loaded from the server
+ */
+export const remoteConfig = ref<RemoteConfig>({})
+
+/**
+ * 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 = {}
+  }
+}

src/platform/remoteConfig/types.ts

@@ -0,0 +1,19 @@
+/**
+ * Server health alert configuration from the backend
+ */
+type ServerHealthAlert = {
+  message: string
+  tooltip?: string
+  severity?: 'info' | 'warning' | 'error'
+  badge?: string
+}
+
+/**
+ * Remote configuration type
+ * Configuration fetched from the server at runtime
+ */
+export type RemoteConfig = {
+  mixpanel_token?: string
+  subscription_required?: boolean
+  server_health_alert?: ServerHealthAlert
+}