fix: remove unnecessary margins from v-main for consistent layout

[Saramanda9988]

Modifications / 改动点

问题来自 dashboard/src/scss/layout/_container.scss 中根布局 .v-main 的固定右外边距。

这个额外的外边距会把背景色显露出来，因此视觉上看起来像右侧多了一条边框，在深色模式下比较明显，且似乎没有具体的作用

修改为无额外边距，保证视觉一致性

• This is NOT a breaking change. / 这不是一个破坏性变更。

Screenshots or Test Results / 运行截图或测试结果

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Checklist / 检查清单

• 😊 If there are new features added in the PR, I have discussed it with the authors through issues/emails, etc.
  / 如果 PR 中有新加入的功能，已经通过 Issue / 邮件等方式和作者讨论过。

• 👀 My changes have been well-tested, and "Verification Steps" and "Screenshots" have been provided above.
  / 我的更改经过了良好的测试，并已在上方提供了“验证步骤”和“运行截图”。

• 🤓 I have ensured that no new dependencies are introduced, OR if new dependencies are introduced, they have been added to the appropriate locations in requirements.txt and pyproject.toml.
  / 我确保没有引入新依赖库，或者引入了新依赖库的同时将其添加到 requirements.txt 和 pyproject.toml 文件相应位置。

• 😮 My changes do not introduce malicious code.
  / 我的更改没有引入恶意代码。

Summary by Sourcery

Remove extra margins from the main layout container to align content consistently with the background across viewports.

Bug Fixes:

• Eliminate the fixed right margin on the main layout to prevent an unintended visible strip at the page edge, especially in dark mode.

Enhancements:

• Standardize the .v-main container margins to zero for consistent layout spacing on both desktop and smaller screens.

[sourcery-ai]

Hey - I've left some high level feedback:

• Since .v-main now has the same margin: 0 rule for both default and @media (max-width: 1279px), consider removing the redundant media-query override or only keeping it if you expect different margins again in the future.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Since `.v-main` now has the same `margin: 0` rule for both default and `@media (max-width: 1279px)`, consider removing the redundant media-query override or only keeping it if you expect different margins again in the future.

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[gemini-code-assist]

Code Review

This pull request updates the SCSS layout by setting the margin of the .v-main container to zero. A review comment suggests removing a redundant media query block, as the base style now covers the margin requirement for all screen sizes.