feat: migrate to OpenCode SDK v2

Update all import statements to use @opencode-ai/sdk/v2
Modify Vite configurations to alias new SDK path
Update API client method signatures for SDK v2 compatibility

packages/ui/src/components/chat/message/parts/AssistantTextPart.tsx

@@ -1,5 +1,5 @@
 import React from 'react';
-import type { Part } from '@opencode-ai/sdk';
+import type { Part } from '@opencode-ai/sdk/v2';
 import { MarkdownRenderer } from '../../MarkdownRenderer';
 import type { StreamPhase } from '../types';
 import type { ContentChangeReason } from '@/hooks/useChatScrollManager';