chore: remove @ai-sdk dependencies and legacy LLM service implementations

- Remove @ai-sdk/google, @ai-sdk/openai, ai packages from dependencies
- Delete SDK-based service files: gemini.ts, openai-compatible.ts, sdkUtils.ts
- Clean up unused types from llm/types.ts (ChatMessage, ChatOptions, LLMConfig, ILLMService, etc.)

package.json

@@ -30,8 +30,6 @@
     "postinstall": "electron-rebuild"
   },
   "dependencies": {
-    "@ai-sdk/google": "^3.0.10",
-    "@ai-sdk/openai": "^3.0.12",
     "@aptabase/electron": "^0.3.1",
     "@electron-toolkit/preload": "^3.0.1",
     "@electron-toolkit/utils": "^4.0.0",
@@ -41,7 +39,6 @@
     "@tanstack/vue-virtual": "^3.13.18",
     "@types/markdown-it": "^14.1.2",
     "@zumer/snapdom": "^2.0.1",
-    "ai": "^6.0.41",
     "better-sqlite3": "^12.4.6",
     "echarts": "^6.0.0",
     "echarts-wordcloud": "^2.1.0",