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/scripts/api.featureFlags.test.ts

@@ -233,4 +233,37 @@ describe('API Feature Flags', () => {
       expect(flag.value).toBe(true)
     })
   })
+
+  describe('Dev override via localStorage', () => {
+    afterEach(() => {
+      localStorage.clear()
+    })
+
+    it('getServerFeature returns localStorage override over server value', () => {
+      api.serverFeatureFlags.value = { some_flag: false }
+      localStorage.setItem('ff:some_flag', 'true')
+
+      expect(api.getServerFeature('some_flag')).toBe(true)
+    })
+
+    it('serverSupportsFeature returns localStorage override over server value', () => {
+      api.serverFeatureFlags.value = { some_flag: false }
+      localStorage.setItem('ff:some_flag', 'true')
+
+      expect(api.serverSupportsFeature('some_flag')).toBe(true)
+    })
+
+    it('getServerFeature falls through when no override is set', () => {
+      api.serverFeatureFlags.value = { some_flag: 'server_value' }
+
+      expect(api.getServerFeature('some_flag')).toBe('server_value')
+    })
+
+    it('getServerFeature override works with numeric values', () => {
+      api.serverFeatureFlags.value = { max_upload_size: 100 }
+      localStorage.setItem('ff:max_upload_size', '999')
+
+      expect(api.getServerFeature('max_upload_size')).toBe(999)
+    })
+  })
 })