Synchronize User Guide from volcano/docs to website with navigation

[Copilot]

Adds 25 User Guide documents from volcano-sh/volcano/docs/user-guide to the website documentation.

Changes

• Content: Copied 25 markdown guides covering scheduler configuration, GPU management (sharing/vGPU/number), plugins (MPI/PyTorch/Ray/SSH/SVC/Env/CDP), NUMA, DRA, network topology, performance tuning, and job policies
• Structure: Created /content/en/docs/user-guide/ with index page and Hugo frontmatter for all guides using [menu.user-guide] to satisfy theme requirements
• Navigation: Added "User Guide" section to docs menu in menus.toml and languages.toml (EN: "User Guide", ZH: "用户指南") for all versions (latest, v1.7.0-v1.12.0), positioned between Ecosystem and Scheduler sections
• Theme compatibility: Configured submenu structure with proper URL references (/en/docs/user-guide/) to work with Academic theme's directory-based menu detection

Site builds successfully with 294 total pages. User Guide accessible at /en/docs/user-guide/ with sidebar navigation across all 25 guides.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Synchronize Volcano User Guide from docs to website and add a new User Guide chapter</issue_title>
<issue_description>The Volcano main repository contains a detailed User Guide under docs/user-guide.

We should synchronize the content of the User Guide from volcano-sh/volcano (https://github.com/volcano-sh/volcano/tree/main/docs/user-guide) to the volcano-sh/website project( and we can add a sync workflow to update the user guide also into website docs, but we can do that in the future). The website should add a new chapter dedicated to the User Guide.

Acceptance Criteria:

• All sections of the User Guide from volcano-sh/volcano are copied and integrated into volcano-sh/website.
• A new "User Guide" chapter is created in the website navigation/menu.
• Content is presented clearly and formatted appropriately for web consumption.

References:

• Volcano User Guide (source)</issue_description>

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

• Fixes Synchronize Volcano User Guide from docs to website and add a new User Guide chapter #467

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[JesseStutler]

I think #472 is better, close