Initial commit: Brass & Sigil monorepo

Self-hosted Minecraft modpack distribution + administration system.

- launcher/  Avalonia 12 desktop client; single-file win-x64 publish.
             Microsoft auth via XboxAuthNet, manifest+SHA-1 mod sync,
             portable install path, sidecar settings.
- server/    brass-sigil-server daemon (.NET 8, linux-x64). Wraps the
             MC subprocess, embedded Kestrel admin panel with cookie
             auth + rate limiting, RCON bridge, scheduled backups,
             BlueMap CLI integration with player markers + skin proxy,
             friend-side whitelist request flow, world wipe with seed
             selection (keep current / random / custom).
- pack/      pack.lock.json (Modrinth + manual CurseForge entries),
             data-only tweak source under tweaks/, build outputs in
             overrides/ (gitignored).
- scripts/   Build-Pack / Build-Tweaks / Update-Pack / Check-Updates
             plus Deploy-Brass.ps1 unified one-shot deploy with
             version-bump pre-flight and daemon-state detection.

launcher/Services/FileLog.cs

@@ -0,0 +1,45 @@
+using System;
+using System.IO;
+
+namespace ModpackLauncher.Services;
+
+public static class FileLog
+{
+    private static readonly object _lock = new();
+
+    public static string LogPath { get; } = BuildPath();
+
+    private static string BuildPath()
+    {
+        var dir = Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
+            "BrassAndSigil"
+        );
+        Directory.CreateDirectory(dir);
+        return Path.Combine(dir, "launcher.log");
+    }
+
+    public static void Init()
+    {
+        try
+        {
+            // Truncate per launch so we always have the most recent run.
+            File.WriteAllText(LogPath,
+                $"=== ModpackLauncher launched {DateTime.Now:yyyy-MM-dd HH:mm:ss} ==={Environment.NewLine}");
+        }
+        catch { }
+    }
+
+    public static void Write(string message)
+    {
+        try
+        {
+            lock (_lock)
+            {
+                File.AppendAllText(LogPath,
+                    $"[{DateTime.Now:HH:mm:ss}] {message}{Environment.NewLine}");
+            }
+        }
+        catch { }
+    }
+}