feat: [additional] Notion 검색 기능 추가

- NotionService: Notion API 검색 + Gemini AI 답변
- AiConfig에 notion provider 추가
- 추가기능 > Notion 검색 채팅 UI

app/Http/Controllers/Additional/NotionSearchController.php

@@ -0,0 +1,51 @@
+<?php
+
+namespace App\Http\Controllers\Additional;
+
+use App\Http\Controllers\Controller;
+use App\Services\NotionService;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+use Illuminate\Http\Response;
+use Illuminate\View\View;
+
+class NotionSearchController extends Controller
+{
+    /**
+     * Notion 검색 페이지 (채팅 UI)
+     */
+    public function index(Request $request): View|Response
+    {
+        if ($request->header('HX-Request')) {
+            return response('', 200)->header('HX-Redirect', route('additional.notion-search.index'));
+        }
+
+        return view('additional.notion-search.index');
+    }
+
+    /**
+     * AJAX 검색 API
+     */
+    public function search(Request $request): JsonResponse
+    {
+        $validated = $request->validate([
+            'message' => 'required|string|max:1000',
+            'history' => 'nullable|array',
+        ]);
+
+        try {
+            $service = new NotionService;
+            $result = $service->searchWithAi(
+                $validated['message'],
+                $validated['history'] ?? []
+            );
+
+            return response()->json($result);
+        } catch (\RuntimeException $e) {
+            return response()->json([
+                'reply' => $e->getMessage(),
+                'debug' => null,
+            ]);
+        }
+    }
+}