Add VS Code Dark+ theme, Chinese IME, autocomplete, and video post-processing

[syk1411119]

概述

本 PR 为 CodeVideoRenderer 增加一组新功能，让代码动画更贴近真实编码体验：

1. VS Code Dark+ 语法高亮

新增 vscode-dark-plus Pygments 样式与 Python 词法器，逐 token 对齐 VS Code Dark+ 配色
（关键字 #569CD6/#C586C0、字符串 #CE9178、函数 #DCDCAA、类 #4EC9B0、注释 #6A9955、数字 #B5CEA8），并设为默认 formatter_style。

2. VS Code 风格自动补全

触发 def/import/class/if/return 等关键词时弹出 IntelliSense 风格补全框：彩色 Codicon 风格图标（方法 ƒ、类 ▣、关键字 ⚿、片段 ➤ 等）、标签、灰色类型说明与蓝色选中行高亮。

3. 中文拼音输入法模拟

新增 chinese_ime 参数，输入中文时弹出拼音候选框，多字词拼音用横杠分隔（世界 → shi-jie）。

4. 退格式代码删除

新增 clear_code / clear_code_mode='backspace'，打完代码后像按退格键一样逐字符删除（速度可调），删除前自动回拉镜头保持画面稳定。

5. 视频后处理助手

新增 postprocess.py：去/加字幕、混背景音乐、拼接、画质/分辨率/fps 设置、加水印、片头、封面、提取/移除音频、裁剪、变速。

其他

• 新增 chinese_ime / ime_wait_time 参数
• formatter_style 默认值改为 vscode-dark-plus
• 依赖新增 pypinyin>=0.49.0，版本号升至 1.5.0
• README 补充文档，测试增至 29 个且全部通过

[ExploreMaths]

请保证项目注释及docstring均为英语（拼音库除外），另外能否提供一些视频以及图片看看效果？

[syk1411119]

Thanks for the review — both points are addressed.

1. Comments & docstrings are now in English

Commit 822fd60 translates all Chinese comments/docstrings to English in
renderer.py, utils.py, vscode_theme.py, postprocess.py, version.py,
__init__.py, and config.py.

Only ime.py is intentionally left in Chinese (the pinyin library you exempted),
plus the Chinese string literals in tests/test_basic.py, which are test data
for the CJK/IME feature rather than comments.

2. Demo — video & images

A short demo rendered with formatter_style='vscode-dark-plus', autocomplete, and
Chinese IME enabled (1280×720 @ 30 fps).

VS Code Dark+ syntax highlighting (final frame — keywords/strings/functions colored like VS Code Dark+):

Autocomplete popup (triggered by def, Codicon-style icons + detail text + selection highlight):

Chinese IME candidate box (pinyin + candidates while typing 你好):

Animated demo (GIF):

Full demo video: demo_showcase.mp4

These assets are also committed under docs/demo/ in this PR.

[ExploreMaths]

AI写的吧，候选框这么大，右侧文本都没对齐，完全不美观啊

[syk1411119]

Quick follow-up: the suggestion/IME popups were a bit oversized and the detail text wasn't row-aligned, so I refined the layout — smaller fonts, a tighter label↔detail gap, detail right-aligned per row, and the box centered under the cursor.

Updated screenshots:

Autocomplete (compact, detail right-aligned):

Chinese IME candidate box:

VS Code Dark+ highlighting (final frame):

Animated demo: demo_showcase.gif · Full video: demo_showcase.mp4

[ExploreMaths]

你能不用AI吗，再用AI我要骂你了

[syk1411119]

......自己写的，还在路上