feat: agent mode tool-calling via Vercel AI SDK

[gabrielste1n]

Summary

• Migrate agent mode streaming from manual fetch/SSE to Vercel AI SDK streamText() with stepCountIs() for multi-step tool calling
• Add unified AI provider factory supporting OpenAI, Groq, Anthropic, Gemini, and custom endpoints
• Add tool registry with search notes, web search, clipboard copy, and calendar tools
• Remove manual AgentLoop (185 lines) in favor of AI SDK's built-in step management

Changes

New files:

• src/services/ai/providers.ts — getAIModel() factory wrapping all AI SDK providers
• src/services/tools/ — ToolRegistry, searchNotesTool, webSearchTool, calendarTool, clipboardTool

Modified:

• src/services/ReasoningService.ts — Add processTextStreamingAI() with tool support, AgentStreamChunk type with content/tool_calls/tool_result/done variants
• src/components/AgentOverlay.tsx — 3 streaming paths (tools/cloud/BYOK), mounted ref guard, AudioManager cleanup, proper tool-result display
• src/services/tools/ToolRegistry.ts — toAISDKFormat() with error handling via try/catch

Deleted:

• src/services/AgentLoop.ts — Replaced by AI SDK stepCountIs()

Details:

• Groq models with disableThinking flag pass providerOptions: { groq: { reasoningEffort: "none" } }
• Tool execution errors return { error } to AI SDK instead of throwing
• Stream loops break on unmount via mountedRef to prevent state updates on unmounted component
• AudioManager properly cleaned up on overlay unmount
• All 5 AI SDK packages added: ai, @ai-sdk/openai, @ai-sdk/groq, @ai-sdk/anthropic, @ai-sdk/google

Test plan

• Verify agent chat works with OpenAI, Groq, Anthropic, Gemini providers
• Verify tool calling works (search notes, web search, clipboard, calendar)
• Verify tool results display in UI (not hardcoded "Done")
• Verify Groq Qwen3 32B works without thinking mode errors
• Verify cloud agent mode still works (IPC path unchanged)
• Verify local model fallback still works
• Verify closing overlay mid-stream doesn't cause React warnings
• Verify custom OpenAI-compatible endpoints work