Fix tab layout, rename tabs, and fix diff rendering double-escaping

[Copilot]

Addresses UI/UX issues with tab positioning, naming, and a diff rendering bug caused by double-escaping content.

Changes

Tab Layout & Naming

• Moved tabs from top to bottom using CSS order: 1
• Renamed "Visual Diff" → "Visual", "Raw Content" → "Content"
• Updated all i18n files (en, zh-cn, ja)

Content Tab Behavior

• Now opens file in VS Code's native text editor instead of displaying raw text in webview

vscode.commands.executeCommand('vscode.openWith', document.uri, 'default');

Diff Rendering Fix

Content was double-escaped: escapeForJs() escaped special chars, then JSON.stringify() escaped them again, corrupting diff content.

Before:

const escapedContent = escapeForJs(content);
let currentContent = ${JSON.stringify(escapedContent)};

After:

let currentContent = ${JSON.stringify(content)};

i18n Note

package.nls.json files must remain in root per VS Code requirements. For runtime webview localization, use @vscode/l10n with l10n/ folder.

Original prompt

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This section details on the original issue you should resolve

<issue_title>问题修复</issue_title>
<issue_description>1. tab移到下面
2. 第一个tab叫Visual 第二个叫Content
3. 第二个编辑器用vscode内置文本编辑器打开文件
4. 第一个tab加载patch/diff 有错误: Unable to render diff. Please check if the content is a valid diff/patch format.
5. 国际化文件能单独放在一个文件夹下么？还是必须放在根目录下</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes 问题修复 #4

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