feat: Add AI-powered commit message generation with jujutsu integration

- Added `json_extract` module to convert structured text to JSON using LOCAL_LLM_API
- Implemented robust error handling for API failures and malformed responses
- Added markdown backtick stripping to ensure clean JSON parsing
- Integrated AI-driven commit message generation via `jj_commit_message()` and `jj_auto_describe()`
- Provided comprehensive unit tests for all core functions
- Added support for custom/local LLM endpoints with fallback to default URL

src/json_extract/__init__.py

@@ -0,0 +1,76 @@
+import json
+import os
+import urllib.request
+import urllib.error
+from typing import Dict, List, Optional
+
+
+def structure_to_json(text: str, schema: Dict) -> Dict:
+    """
+    Convert structured text to JSON using LOCAL_LLM_API.
+
+    Args:
+        text (str): The structured text to convert
+        schema (dict): The JSON schema to use for conversion
+
+    Returns:
+        dict: The parsed JSON object
+    """
+    # Get the API URL from environment variable
+    local_llm_api = os.environ.get("LOCAL_LLM_API", "http://host.docker.internal:1248/v1")
+    
+    # Format the schema as JSON string
+    schema_json = json.dumps(schema, indent=2)
+    
+    # Create the prompt following the pattern from jj-ai-commit.sh
+    prompt_text = f"""Analyse this text and respond ONLY with a valid JSON object matching the schema.
+
+Text:
+{text}
+
+Schema:
+{schema_json}"""
+    
+    # Build the request body
+    request_body = {
+        "model": "qwen3-coder",
+        "messages": [
+            {"role": "user", "content": prompt_text}
+        ]
+    }
+    
+    # Build the URL
+    url = f"{local_llm_api}/chat/completions"
+    
+    # Create the request
+    data = json.dumps(request_body).encode("utf-8")
+    req = urllib.request.Request(
+        url,
+        data=data,
+        headers={"Content-Type": "application/json"},
+        method="POST"
+    )
+    
+    try:
+        # Execute the request
+        with urllib.request.urlopen(req) as response:
+            result = json.loads(response.read().decode("utf-8"))
+    except urllib.error.URLError as e:
+        return {"error": f"API request failed: {e}", "raw_response": ""}
+    except json.JSONDecodeError as e:
+        return {"error": f"Failed to parse response: {e}", "raw_response": ""}
+    
+    try:
+        content = result.get("choices", [{}])[0].get("message", {}).get("content", "")
+        
+        # Clean markdown backticks from response
+        clean_content = content.strip()
+        while clean_content.startswith("`") or clean_content.startswith("```"):
+            clean_content = clean_content[1:].strip()
+        while clean_content.endswith("`") or clean_content.endswith("```"):
+            clean_content = clean_content[:-1].strip()
+        
+        # Parse the JSON content
+        return json.loads(clean_content)
+    except (json.JSONDecodeError, KeyError, IndexError) as e:
+        return {"error": f"Failed to parse JSON: {e}", "raw_response": json.dumps(result)}