feat(backend): Fix client-profile endpoint and add attachment support

- Fixed client-profile GET endpoint to prevent 500 errors
- Made ClientProfileResponse fields optional (id, created_at, updated_at)
- Returns empty profile data instead of creating DB entry on GET
- Added new attachment model and schemas for file handling
- Added file handler core utility for upload management

backend/app/core/file_handler.py

@@ -0,0 +1,101 @@
+"""
+File Handler - ServiceManagerWeb  
+Gestión simple de archivos adjuntos
+"""
+import os
+import uuid
+import hashlib
+from pathlib import Path
+from typing import Tuple
+from fastapi import UploadFile, HTTPException, status
+
+from app.core.config import get_settings
+
+settings = get_settings()
+
+
+class FileHandler:
+    """Handler simple para archivos adjuntos"""
+    
+    def __init__(self):
+        self.upload_path = Path(settings.UPLOAD_PATH)
+        self.max_size_bytes = settings.MAX_UPLOAD_SIZE_MB * 1024 * 1024
+        self.allowed_extensions = settings.ALLOWED_FILE_EXTENSIONS
+        # Crear directorio si no existe
+        self.upload_path.mkdir(parents=True, exist_ok=True)
+    
+    def _validate_file(self, filename: str, file_size: int) -> None:
+        """Validar archivo"""
+        extension = Path(filename).suffix.lower().lstrip('.')
+        
+        if extension not in self.allowed_extensions:
+            raise HTTPException(
+                status_code=status.HTTP_400_BAD_REQUEST,
+                detail=f"Extensión no permitida: {extension}"
+            )
+        
+        if file_size > self.max_size_bytes:
+            raise HTTPException(
+                status_code=status.HTTP_413_REQUEST_ENTITY_TOO_LARGE,
+                detail=f"Archivo muy grande. Máximo: {settings.MAX_UPLOAD_SIZE_MB}MB"
+            )
+    
+    def _calculate_checksums(self, content: bytes) -> Tuple[str, str]:
+        """Calcular MD5 y SHA256"""
+        return hashlib.md5(content).hexdigest(), hashlib.sha256(content).hexdigest()
+    
+    async def save_upload(self, file: UploadFile, tenant_id: uuid.UUID, ticket_id: uuid.UUID) -> dict:
+        """Guardar archivo y retornar metadata"""
+        if not file.filename:
+            raise HTTPException(status_code=400, detail="Filename requerido")
+        
+        content = await file.read()
+        file_size = len(content)
+        
+        self._validate_file(file.filename, file_size)
+        
+        md5_hash, sha256_hash = self._calculate_checksums(content)
+        
+        # Nombre único
+        extension = Path(file.filename).suffix.lower()
+        safe_filename = f"{uuid.uuid4().hex}{extension}"
+        
+        # Estructura: uploads/tenant_id/tickets/ticket_id/
+        file_directory = self.upload_path / str(tenant_id) / "tickets" / str(ticket_id)
+        file_directory.mkdir(parents=True, exist_ok=True)
+        
+        file_path = file_directory / safe_filename
+        relative_path = str(file_path.relative_to(self.upload_path))
+        
+        # Guardar archivo
+        with open(file_path, "wb") as f:
+            f.write(content)
+        
+        import mimetypes
+        mime_type = mimetypes.guess_type(file.filename)[0] or "application/octet-stream"
+        
+        return {
+            "filename": safe_filename,
+            "original_filename": file.filename,
+            "file_path": relative_path,
+            "file_size": file_size,
+            "mime_type": mime_type,
+            "md5_hash": md5_hash,
+            "sha256_hash": sha256_hash
+        }
+    
+    def get_file_path(self, relative_path: str) -> Path:
+        """Obtener path absoluto del archivo"""
+        file_path = (self.upload_path / relative_path).resolve()
+        
+        # Verificar que no escape del directorio de uploads
+        if not str(file_path).startswith(str(self.upload_path.resolve())):
+            raise HTTPException(status_code=403, detail="Acceso denegado")
+        
+        if not file_path.exists():
+            raise HTTPException(status_code=404, detail="Archivo no encontrado")
+        
+        return file_path
+
+
+file_handler = FileHandler()