feat: add unified usage popover with Claude and Codex tabs

- Created combined UsagePopover component with tab switching between providers
- Added Codex usage API endpoint and service (returns not available message)
- Updated BoardHeader to show single usage button for both providers
- Enhanced type definitions for Codex usage with primary/secondary rate limits
- Wired up Codex usage API in HTTP client

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/ui/src/lib/http-api-client.ts

@@ -36,7 +36,7 @@ import type {
   ConvertToFeatureOptions,
 } from './electron';
 import type { Message, SessionListItem } from '@/types/electron';
-import type { Feature, ClaudeUsageResponse } from '@/store/app-store';
+import type { Feature, ClaudeUsageResponse, CodexUsageResponse } from '@/store/app-store';
 import type { WorktreeAPI, GitAPI, ModelDefinition, ProviderStatus } from '@/types/electron';
 import { getGlobalFileBrowser } from '@/contexts/file-browser-context';
 
@@ -1834,6 +1834,11 @@ export class HttpApiClient implements ElectronAPI {
     getUsage: (): Promise<ClaudeUsageResponse> => this.get('/api/claude/usage'),
   };
 
+  // Codex API
+  codex = {
+    getUsage: (): Promise<CodexUsageResponse> => this.get('/api/codex/usage'),
+  };
+
   // Context API
   context = {
     describeImage: (