Azure DevOps instance URL fails when protocol is included

## Description
When configuring the Azure DevOps instance setting, if users include the protocol (http:// or https://) in the URL, the plugin fails with a DNS resolution error.

## Current Behavior
- Entering \ in the instance field causes \ error
- The URL becomes malformed: \

## Expected Behavior
- The plugin should automatically strip any protocol prefix from the instance URL
- Clear guidance should be provided about the expected format

## Steps to Reproduce
1. Go to plugin settings
2. Enter \ in the Instance field
3. Try to sync or update tasks
4. Observe DNS resolution error in console

## Environment
- Obsidian version: Latest
- Plugin version: 1.4.0
- Azure DevOps type: Cloud (dev.azure.com)

The payload does not name a file or test; start at the plugin settings Instance field and trace the Azure DevOps sync/update path that consumes it. Verify the reproduction with both protocol-prefixed values, then confirm syncing works and the settings guidance states the accepted format.

Written by the indexing model from the issue text.