feat: Adds Build Tool for Publishing/Setup (#2392)

## Summary

Replaces the basic `publish.cmd`/`publish.sh` scripts with an interactive **BuildTool** — a C# console app using [Spectre.Console](https://spectreconsole.net/) that guides users through publishing, prerequisite checking, and cross-compilation.

### Why
The community found the existing publish scripts unhelpful for newcomers. They worked but didn't walk users through the process, didn't check prerequisites, and provided no feedback when things went wrong.

### What's New

**Interactive BuildTool** (`Projects/BuildTool/`)
- NativeAOT-compiled C# console app with true-color ASCII logo and ModernUO brand gold/silver palette
- Guided publish wizard with step-by-step back navigation (Ctrl+C or menu "Back" to go to previous step)
- Prerequisite checking: .NET SDK version, VC++ Redistributable (Windows), native libraries (Linux/macOS)
- .NET SDK auto-install offer via Microsoft's official install scripts
- Platform detection: Windows 10 vs 11 (build number), macOS codenames, Linux distro + kernel version
- Cross-compilation support: skips native library checks, shows target prerequisites after build
- Non-interactive mode for CI: `--config Release --skip-prereqs`
- Backward-compatible positional args: `publish.cmd release win x64` still works

**Shell Wrappers** (`publish.cmd`, `publish.ps1`, `publish.sh`)
- Try native BuildTool binary first (downloaded from GitHub Releases)
- Fall back to `dotnet run --project Projects/BuildTool` if unavailable
- SDK bootstrapping: offer to install .NET if not found

**CI/CD Updates**
- Build/test workflows target `Projects/Application/Application.csproj` instead of the solution (excludes BuildTool and test projects from publish)
- New `build-tool-release.yml` workflow builds NativeAOT binaries for win-x64, win-arm64, osx-arm64, linux-x64, linux-arm64
- Minimum SDK bumped to 10.0.201 (required for Serialization Generator 2.14.3 / Roslyn 5.3.0)

**Other Changes**
- Solution converted from `.sln` to `.slnx`
- Updated README with interactive mode instructions and deployment guidance

## Screenshots

<img width="320" height="378" alt="image" src="https://github.com/user-attachments/assets/83c057c5-3992-4dbd-99fa-0e3c24ef6428" />

<img width="749" height="554" alt="image" src="https://github.com/user-attachments/assets/e4ee4d6f-71d4-47f9-86b6-8fd1ca3c3e7a" />

Projects/BuildTool/Interactive/CancellationTracker.cs

@@ -0,0 +1,25 @@
+namespace BuildTool.Interactive;
+
+/// <summary>
+/// Tracks Ctrl+C press timing to detect double-press for exit.
+/// </summary>
+public sealed class CancellationTracker
+{
+    private DateTime _lastCancelTime = DateTime.MinValue;
+    private const int DoublePressMs = 500;
+
+    /// <summary>
+    /// Checks if this is a double-press (within 500ms of last press).
+    /// Also updates the last press time.
+    /// </summary>
+    public bool IsDoublePress()
+    {
+        var now = DateTime.UtcNow;
+        var isDouble = (now - _lastCancelTime).TotalMilliseconds < DoublePressMs;
+        _lastCancelTime = now;
+        return isDouble;
+    }
+
+    /// <summary>Global instance for app-wide tracking.</summary>
+    public static CancellationTracker Instance { get; } = new();
+}