feat: implement Dropbox integration with OAuth setup and error handling

app/frontend.py

@@ -159,3 +159,60 @@ async def onedrive_callback(request: Request, code: str = None, error: str = Non
         }
     )
 
+@router.get("/dropbox-setup")
+@require_login
+async def dropbox_setup_page(request: Request):
+    """
+    Setup page for the Dropbox integration.
+    Shows configuration status and setup instructions.
+    """
+    # Check Dropbox configuration
+    is_configured = bool(settings.dropbox_app_key and 
+                         settings.dropbox_app_secret and 
+                         settings.dropbox_refresh_token)
+    
+    return templates.TemplateResponse(
+        "dropbox.html",
+        {
+            "request": request,
+            "is_configured": is_configured,
+            "app_key_value": settings.dropbox_app_key or "",
+            "app_secret_value": settings.dropbox_app_secret if settings.dropbox_app_secret else "",
+            "refresh_token_value": settings.dropbox_refresh_token if settings.dropbox_refresh_token else "",
+            "folder_path": settings.dropbox_folder or "/Documents/Uploads"  # Default folder path
+        }
+    )
+
+@router.get("/dropbox-callback")
+@require_login
+async def dropbox_callback(request: Request, code: str = None, error: str = None):
+    """
+    Callback endpoint for Dropbox OAuth flow.
+    Automatically exchanges the code for a token and saves it to the configuration.
+    """
+    if error:
+        return templates.TemplateResponse(
+            "dropbox_callback_error.html",
+            {"request": request, "error": error}
+        )
+    
+    if not code:
+        return templates.TemplateResponse(
+            "dropbox_callback_error.html",
+            {"request": request, "error": "No authorization code received from Dropbox"}
+        )
+    
+    # Display the processing page with automatic token exchange
+    # Note: We provide empty strings for app_key_value and app_secret_value
+    # to prevent overriding what's in sessionStorage
+    return templates.TemplateResponse(
+        "dropbox_callback.html",
+        {
+            "request": request, 
+            "code": code,
+            "app_key_value": "",  # The callback will prioritize sessionStorage values
+            "app_secret_value": "",  # The callback will prioritize sessionStorage values
+            "folder_path": ""  # The callback will prioritize sessionStorage values
+        }
+    )
+