Add package structure and resource path utilities

- Created langbot/ package with __init__.py and __main__.py entry point
- Added paths utility to find frontend and resource files from package installation
- Updated config loading to use resource paths
- Updated frontend serving to use resource paths
- Added MANIFEST.in for package data inclusion
- Updated pyproject.toml with build system and entry points

Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

pkg/config/impls/json.py

@@ -18,12 +18,22 @@ class JSONConfigFile(file_model.ConfigFile):
         self.template_file_name = template_file_name
         self.template_data = template_data
 
+    def _get_template_path(self) -> str:
+        """Get the actual path to the template file, handling package installation"""
+        if self.template_file_name is None:
+            return None
+        
+        from ...utils import paths as path_utils
+        return path_utils.get_resource_path(self.template_file_name)
+
     def exists(self) -> bool:
         return os.path.exists(self.config_file_name)
 
     async def create(self):
-        if self.template_file_name is not None:
-            shutil.copyfile(self.template_file_name, self.config_file_name)
+        template_path = self._get_template_path()
+        
+        if template_path is not None:
+            shutil.copyfile(template_path, self.config_file_name)
         elif self.template_data is not None:
             with open(self.config_file_name, 'w', encoding='utf-8') as f:
                 json.dump(self.template_data, f, indent=4, ensure_ascii=False)
@@ -34,8 +44,10 @@ class JSONConfigFile(file_model.ConfigFile):
         if not self.exists():
             await self.create()
 
-        if self.template_file_name is not None:
-            with open(self.template_file_name, 'r', encoding='utf-8') as f:
+        template_path = self._get_template_path()
+        
+        if template_path is not None:
+            with open(template_path, 'r', encoding='utf-8') as f:
                 self.template_data = json.load(f)
 
         with open(self.config_file_name, 'r', encoding='utf-8') as f: