docs: Add warning for uv usage on Windows (symlink compatibility)

[Creative-Geek]

Description

This PR adds a warning to the uv installation guide regarding a specific compatibility issue on Windows.

The Problem

When using uv to manage a Flet project on Windows, running uv run flet run main.py causes the application to exit silently with code 0. No GUI window appears, and no error is thrown. Setting FLET_LOG_LEVEL=debug produces no output.

Investigation (Skip Reading This)

I encountered this issue personally and went through extensive debugging:

1. Verification: Validated that the exact same script works perfectly when using a standard venv created by python -m venv.
2. Environment: Tested across different terminals (Git Bash, PowerShell, CMD) with the same silent failure result.
3. Dependencies: Attempted pinning Python versions and websockets versions to rule out library conflicts.
4. Root Cause: I discovered that the issue stems from how uv links packages in the virtual environment. Flet's internal logic for locating its binaries/assets fails when uv uses symbolic links on Windows.

The Solution

The issue is resolved by forcing uv to physically copy files instead of linking them. Configuring [tool.uv] link-mode = "copy" in pyproject.toml fixes the silent crash immediately.

Changes

• Added a :::warning block to the uv section of the Getting Started guide (which is the only place where uv is directly mentioned).

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