feat(123): allow modification of the platform header

[moyanj]

Description / 描述

允许修改platform请求头以支持部分特殊场景

Motivation and Context / 背景

How Has This Been Tested? / 测试

已在本地手动测试

Checklist / 检查清单

• I have read the CONTRIBUTING document.
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• I have formatted my code with go fmt or prettier.
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• I have added appropriate labels to this PR (or mentioned needed labels in the description if lacking permissions).
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• I have requested review from relevant code authors using the "Request review" feature when applicable.
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• I have updated the repository accordingly (If it’s needed).
  我已相应更新了相关仓库（若适用）。
  • OpenList-Frontend #XXXX
  • OpenList-Docs #XXXX

[Copilot]

Pull Request Overview

This PR adds support for customizing the platform HTTP header in the 123 driver to accommodate special use cases. The change introduces a new configurable field that allows users to specify different platform values instead of the hardcoded "web" value.

Key changes:

• Added a new Platform configuration field to the driver's metadata with a default value of "web"
• Updated the header setting to use the configurable platform value instead of the hardcoded string
• Modified the Init method to explicitly set the platform header to "web" during initialization

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
drivers/123/meta.go	Adds the new Platform configuration field to the Addition struct
drivers/123/util.go	Updates the platform header to use the configurable d.Platform value
drivers/123/driver.go	Modifies Init to explicitly set platform header to "web" for initialization requests

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