Fix Gemini and Mistral provider imports

Switch Gemini from deprecated google-generativeai to google-genai.
Fix Mistral import path to mistralai.client.Mistral (v2.x layout).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

kniepunkt/providers.py

@@ -51,23 +51,24 @@ class GeminiProvider(Provider):
     name = "Gemini"
 
     def __init__(self):
-        import google.generativeai as genai
-        genai.configure(api_key=os.environ["GOOGLE_API_KEY"])
-        self._genai = genai
+        from google import genai
+        from google.genai import types as genai_types
+        self._client = genai.Client(api_key=os.environ["GOOGLE_API_KEY"])
+        self._types = genai_types
 
     def chat(self, messages: list[dict], system: str, max_tokens: int = 4096) -> str:
-        model = self._genai.GenerativeModel(
-            model_name="gemini-2.0-flash",
-            system_instruction=system,
-        )
         # Convert role "assistant" → "model" for Gemini
         contents = [
-            {"role": "model" if m["role"] == "assistant" else "user", "parts": [m["content"]]}
+            {"role": "model" if m["role"] == "assistant" else "user", "parts": [{"text": m["content"]}]}
             for m in messages
         ]
-        response = model.generate_content(
-            contents,
-            generation_config=self._genai.types.GenerationConfig(max_output_tokens=max_tokens),
+        response = self._client.models.generate_content(
+            model="gemini-2.0-flash",
+            contents=contents,
+            config=self._types.GenerateContentConfig(
+                system_instruction=system,
+                max_output_tokens=max_tokens,
+            ),
         )
         return response.text
 
@@ -76,7 +77,7 @@ class MistralProvider(Provider):
     name = "Mistral"
 
     def __init__(self):
-        from mistralai import Mistral
+        from mistralai.client import Mistral
         self._client = Mistral(api_key=os.environ["MISTRAL_API_KEY"])
 
     def chat(self, messages: list[dict], system: str, max_tokens: int = 4096) -> str: