[Feature]: Add tooltips to model library folders with Chinese explanations for beginners (v0.8.36)

### What problem are you experiencing?

When using ComfyUI Desktop (v0.8.36), after opening the application and clicking "模型" (Models) on the left sidebar, the "模型库" (Model Library) heading is correctly displayed in Chinese, but all the directory names in the tree below are in English (e.g., "checkpoints", "diffusers", "loras", "vae", "controlnet", "clip", etc.).

For Chinese-speaking beginners who are not familiar with ComfyUI's model directory structure, it is not obvious what each folder contains or what its purpose is. For example:
- What is the difference between "checkpoints" and "diffusers"?
- What goes in "clip" vs "text_encoders"?
- What is "controlnet" used for?

Additionally, hovering the mouse over each directory entry does not display any tooltip or explanation.

### When does this problem occur?

- Every time the Model Library sidebar tab is opened
- When browsing model directories to find a specific type of model
- The English folder names are visible at all times, affecting every session

### How often do you encounter this problem?

Every time (Multiple times per day)

### How much does this problem affect your workflow?

Causes moderate inconvenience

### Current workarounds

- Users need to search online to understand what each ComfyUI model folder is for
- Experienced users already know the folder structure, but beginners have no way to learn from within the app

### Ideas for solutions (Optional)

Add tooltip text to each model folder/type entry in the tree explorer. When the user hovers over a folder name (e.g., "checkpoints"), a tooltip could explain what that folder contains and what it is used for.

The folder descriptions could be stored as i18n keys so they can be translated into all supported languages. For example, the English descriptions could be mapped to folder names, and each locale would provide localized explanations.

The tooltips would need to be displayed on the folder nodes in the TreeExplorer component, ideally using the existing `v-tooltip` directive used elsewhere in the app.

### Additional context

**Version:** ComfyUI Frontend v0.8.36 (compatible with ComfyUI Desktop v0.8.36)

The folder names come from the ComfyUI server's file system structure. The existing `sideToolbar.modelLibrary` key in locale files correctly translates the section heading, but the individual folder names within the tree are raw server folder names and cannot be directly translated via the current i18n system.

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-11984-Feature-Add-tooltips-to-model-library-folders-with-Chinese-explanations-for-beginn-3576d73d365081519295f3ebd43b6307) by [Unito](https://www.unito.io)