Fix project links and add ISBI2012-UNet to README

[Copilot]

The Brain-Tumor-Segmentation link was pointing to repository root instead of the actual project location. The newly added ISBI2012-UNet project was missing from the project table.

Changes

• Fixed Brain-Tumor-Segmentation link: ./Brain-Tumor-Segmentation → ./DeepLearning/Pytorch/Segmentation/Brain_Tumor_Segmentation
• Added ISBI2012-UNet project: U-Net paper reproduction with ResNet-34, UNet, and UNet++ implementations for ISBI 2012 neuronal structure segmentation
• Cleaned up descriptions: Removed placeholder text and standardized formatting

Updated Table

| **[`Brain-Tumor-Segmentation`](./DeepLearning/Pytorch/Segmentation/Brain_Tumor_Segmentation)** | **脑肿瘤 MRI 图像分割** | UNet | `Segmentation` |
| **[`ISBI2012-UNet`](./DeepLearning/Pytorch/Segmentation/ISBI2012-UNet)** | **ISBI 2012 神经元结构分割** | UNet/UNet++/ResNet | `Segmentation` |

Original prompt

The user wants to update the README.md file in the zlyd-CV/Medical-AI-Projects repository.

The repository structure shows that projects are located in DeepLearning/Pytorch/Segmentation/.
The current README.md contains a table of projects, but the link for Brain-Tumor-Segmentation is incorrect (pointing to root instead of the subfolder) and the new project ISBI2012-UNet (which the user just uploaded as shown in the image ) is missing.

Please update README.md as follows:

1. In the "## 🗂️ 项目列表 (Projects)" section, update the table.
2. Fix the link for Brain-Tumor-Segmentation to be ./DeepLearning/Pytorch/Segmentation/Brain_Tumor_Segmentation.
3. Add a new row for the ISBI2012-UNet project.
   • Name: ISBI2012-UNet
   • Link: ./DeepLearning/Pytorch/Segmentation/ISBI2012-UNet
   • Description: **ISBI 2012 神经元结构分割**。<br>复现 U-Net 论文，包含 ResNet-34, UNet, UNet++ 三种模型实现。
   • Model/Method: UNet/UNet++/ResNet
   • Keywords: `Segmentation`

The resulting table should look like this (preserving the header and the last "Pending" row):

| 📂 项目文件夹 | 📝 项目描述 | 🧠 模型/方法 | 🏷️ 关键词 |
| :--- | :--- | :--- | :--- |
| **[`Brain-Tumor-Segmentation`](./DeepLearning/Pytorch/Segmentation/Brain_Tumor_Segmentation)** | **脑肿瘤 MRI 图像分割**。<br>基于MRI数据集，实现脑肿瘤区域的自动分割，并接入SwanLab实验面板。 | UNet | `Segmentation` |
| **[`ISBI2012-UNet`](./DeepLearning/Pytorch/Segmentation/ISBI2012-UNet)** | **ISBI 2012 神经元结构分割**。<br>复现 U-Net 论文，包含 ResNet-34, UNet, UNet++ 三种模型实现。 | UNet/UNet++/ResNet | `Segmentation` |
| **[`<待更新-分类项目>`](./)** | (计划中) 医学图像二分类/多分类任务 | ResNet/ViT | `Classification` |

Note: I am also slightly refining the description of Brain Tumor Segmentation to replace the truncated/placeholder text with a complete sentence similar to the original context.

This pull request was created from Copilot chat.

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