feat: add dev-time feature flag overrides via localStorage (#9075)

## Summary
- Adds `localStorage`-based dev-time override for feature flags, with
`ff:` key prefix (e.g.
`localStorage.setItem('ff:team_workspaces_enabled', 'true')`)
- Override priority: dev localStorage > remoteConfig >
serverFeatureFlags
- Guarded by `import.meta.env.DEV` — tree-shaken to empty function in
production builds
- Extracts `resolveFlag` helper in `useFeatureFlags` to eliminate
repeated fallback pattern

Fixes #9054

## Test plan
- [x] `getDevOverride` unit tests: boolean/number/string/object parsing,
prefix isolation, invalid JSON warning
- [x] `api.getServerFeature` / `serverSupportsFeature` override tests
- [x] `useFeatureFlags` override priority tests, including
`teamWorkspacesEnabled` bypassing guards
- [x] Production build verified: `getDevOverride` compiles to empty
function body, localStorage never accessed
- [x] `pnpm typecheck`, `pnpm lint` clean

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9075-feat-add-dev-time-feature-flag-overrides-via-localStorage-30f6d73d365081b394d3ccc461987b1a)
by [Unito](https://www.unito.io)

src/composables/useFeatureFlags.ts

@@ -6,6 +6,7 @@ import {
   remoteConfig
 } from '@/platform/remoteConfig/remoteConfig'
 import { api } from '@/scripts/api'
+import { getDevOverride } from '@/utils/devFeatureFlagOverride'
 
 /**
  * Known server feature flags (top-level, not extensions)
@@ -24,6 +25,19 @@ export enum ServerFeatureFlag {
   NODE_REPLACEMENTS = 'node_replacements'
 }
 
+/**
+ * Resolves a feature flag value with dev override > remoteConfig > serverFeature priority.
+ */
+function resolveFlag<T>(
+  flagKey: string,
+  remoteConfigValue: T | undefined,
+  defaultValue: T
+): T {
+  const override = getDevOverride<T>(flagKey)
+  if (override !== undefined) return override
+  return remoteConfigValue ?? api.getServerFeature(flagKey, defaultValue)
+}
+
 /**
  * Composable for reactive access to server-side feature flags
  */
@@ -39,38 +53,40 @@ export function useFeatureFlags() {
       return api.getServerFeature(ServerFeatureFlag.MANAGER_SUPPORTS_V4)
     },
     get modelUploadButtonEnabled() {
-      return (
-        remoteConfig.value.model_upload_button_enabled ??
-        api.getServerFeature(
-          ServerFeatureFlag.MODEL_UPLOAD_BUTTON_ENABLED,
-          false
-        )
+      return resolveFlag(
+        ServerFeatureFlag.MODEL_UPLOAD_BUTTON_ENABLED,
+        remoteConfig.value.model_upload_button_enabled,
+        false
       )
     },
     get assetRenameEnabled() {
-      return (
-        remoteConfig.value.asset_rename_enabled ??
-        api.getServerFeature(ServerFeatureFlag.ASSET_RENAME_ENABLED, false)
+      return resolveFlag(
+        ServerFeatureFlag.ASSET_RENAME_ENABLED,
+        remoteConfig.value.asset_rename_enabled,
+        false
       )
     },
     get privateModelsEnabled() {
-      return (
-        remoteConfig.value.private_models_enabled ??
-        api.getServerFeature(ServerFeatureFlag.PRIVATE_MODELS_ENABLED, false)
+      return resolveFlag(
+        ServerFeatureFlag.PRIVATE_MODELS_ENABLED,
+        remoteConfig.value.private_models_enabled,
+        false
       )
     },
     get onboardingSurveyEnabled() {
-      return (
-        remoteConfig.value.onboarding_survey_enabled ??
-        api.getServerFeature(ServerFeatureFlag.ONBOARDING_SURVEY_ENABLED, false)
+      return resolveFlag(
+        ServerFeatureFlag.ONBOARDING_SURVEY_ENABLED,
+        remoteConfig.value.onboarding_survey_enabled,
+        false
       )
     },
     get linearToggleEnabled() {
       if (isNightly) return true
 
-      return (
-        remoteConfig.value.linear_toggle_enabled ??
-        api.getServerFeature(ServerFeatureFlag.LINEAR_TOGGLE_ENABLED, false)
+      return resolveFlag(
+        ServerFeatureFlag.LINEAR_TOGGLE_ENABLED,
+        remoteConfig.value.linear_toggle_enabled,
+        false
       )
     },
     /**
@@ -80,11 +96,12 @@ export function useFeatureFlags() {
      * and prevents race conditions during initialization.
      */
     get teamWorkspacesEnabled() {
-      if (!isCloud) return false
+      const override = getDevOverride<boolean>(
+        ServerFeatureFlag.TEAM_WORKSPACES_ENABLED
+      )
+      if (override !== undefined) return override
 
-      // Only return true if authenticated config has been loaded.
-      // This prevents race conditions where code checks this flag before
-      // WorkspaceAuthGate has refreshed the config with auth.
+      if (!isCloud) return false
       if (!isAuthenticatedConfigLoaded.value) return false
 
       return (
@@ -93,9 +110,10 @@ export function useFeatureFlags() {
       )
     },
     get userSecretsEnabled() {
-      return (
-        remoteConfig.value.user_secrets_enabled ??
-        api.getServerFeature(ServerFeatureFlag.USER_SECRETS_ENABLED, false)
+      return resolveFlag(
+        ServerFeatureFlag.USER_SECRETS_ENABLED,
+        remoteConfig.value.user_secrets_enabled,
+        false
       )
     },
     get nodeReplacementsEnabled() {