feat: Implement main application shell with navigation and color scheme toggle

- Added Appshell component with responsive navbar and main content area
- Integrated ColorSchemeToggle for light/dark mode switching
- Created Welcome component with styled title and introductory text
- Developed ChatPage for LLM interaction with WebSocket support
- Implemented Biblioteca for managing notes with rich text editor
- Added LoginPage for user authentication with error handling
- Introduced MessageList and MessageBubble components for chat messages
- Styled components with CSS modules for consistent design

domains/ArquitectureLayer/Model.py

@@ -0,0 +1,63 @@
+# src\ArquitectureLayer\Model.py
+
+from sqlalchemy import Column, DateTime, String, Integer, Text, func
+from sqlalchemy.ext.declarative import declared_attr, as_declarative
+from datetime import datetime
+
+@as_declarative()
+class Model_base:
+    __abstract__ = True
+
+    @declared_attr
+    def sys_created_at(cls):
+        return Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+
+    @declared_attr
+    def sys_created_by(cls):
+        return Column(String, nullable=True)
+
+    @declared_attr
+    def sys_updated_at(cls):
+        return Column(DateTime(timezone=True), onupdate=func.now(), nullable=True)
+
+    @declared_attr
+    def sys_updated_by(cls):
+        return Column(String, nullable=True)
+
+    @declared_attr
+    def sys_version(cls):
+        return Column(Integer, default=1, nullable=False)
+
+    @declared_attr
+    def sys_notes(cls):
+        return Column(Text, nullable=True)
+
+    @declared_attr
+    def sys_deleted_at(cls):
+        return Column(DateTime(timezone=True), nullable=True)
+
+    def __repr__(self):
+        id_val = getattr(self, "id", None)
+        return f"<{self.__class__.__name__} id={id_val}>"
+
+    def __str__(self):
+        cls = self.__class__.__name__
+        id_val = getattr(self, "id", None)
+        return f"{cls}(id={id_val})"
+
+    def __json__(self) -> dict:
+        """Devuelve una representación JSON serializable (dict plano)."""
+        out = {}
+
+        # Prevención de error: solo ejecuta si __table__ existe
+        if not hasattr(self, "__table__"):
+            return out
+
+        for attr in self.__table__.columns:
+            val = getattr(self, attr.name, None)
+            if isinstance(val, datetime):
+                out[attr.name] = val.isoformat()
+            else:
+                out[attr.name] = val
+
+        return out