feat: Windows-Kompatibilität

- WorkspaceHelper: Zentrale Hilfsmethoden (IsWindows, TempDir, IsSubPathOf,
  GetRelativePath, ShellExecutable, ShellArguments)
- ToolService: execute nutzt cmd.exe auf Windows, GetRelativePath mit
  Forward-Slashes, IsSubPathOf für case-insensitive Pfadprüfung
- SessionEndpoint: /tmp → Path.GetTempPath(), bash → cmd.exe,
  Fire-and-forget via .bat statt systemd-run auf Windows
- ChatService: /tmp → WorkspaceHelper.TempDir
- MemoryService: IsSubPathOf + GetRelativePath
- WorkspaceEndpoint: HandleBrowse zeigt Laufwerke auf Windows,
  IsSubPathOf statt StartsWith
- InfoEndpoint: gott.exe auf Windows, isWindows-Flag in API-Response
- Frontend: File-Explorer mit Laufwerks-Navigation auf Windows

Endpoints/WorkspaceEndpoint.cs

@@ -9,6 +9,7 @@ using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.DependencyInjection;
+using Gott.Services;
 
 namespace Gott.Endpoints;
 
@@ -83,7 +84,7 @@ public static class WorkspaceEndpoint
 
         var userId = ctx.GetUserId();
         var user = await db.GetUser(userId);
-        var resolved = Gott.Services.WorkspaceHelper.ResolveWorkspace(session, user);
+        var resolved = WorkspaceHelper.ResolveWorkspace(session, user);
         if (string.IsNullOrEmpty(resolved))
         {
             ctx.Response.StatusCode = 400;
@@ -125,7 +126,7 @@ public static class WorkspaceEndpoint
         var subPath = ctx.Request.Query["path"].FirstOrDefault() ?? "";
         var targetPath = Path.GetFullPath(Path.Combine(basePath, subPath));
 
-        if (!targetPath.StartsWith(basePath))
+        if (!WorkspaceHelper.IsSubPathOf(targetPath, basePath))
         {
             ctx.Response.StatusCode = 403;
             return;
@@ -144,7 +145,7 @@ public static class WorkspaceEndpoint
         {
             var name = Path.GetFileName(dir);
             if (IgnoredDirs.Contains(name)) continue;
-            var relPath = Path.GetRelativePath(basePath, dir).Replace('\\', '/');
+            var relPath = WorkspaceHelper.GetRelativePath(basePath, dir);
             entries.Add(new { name, path = relPath, type = "dir" });
         }
 
@@ -152,7 +153,7 @@ public static class WorkspaceEndpoint
         {
             var name = Path.GetFileName(file);
             var ext = Path.GetExtension(file);
-            var relPath = Path.GetRelativePath(basePath, file).Replace('\\', '/');
+            var relPath = WorkspaceHelper.GetRelativePath(basePath, file);
             var size = new FileInfo(file).Length;
             var isText = TextExtensions.Contains(ext) || IsLikelyTextFile(name);
             entries.Add(new { name, path = relPath, type = "file", ext, size, isText });
@@ -173,7 +174,7 @@ public static class WorkspaceEndpoint
         }
 
         var targetPath = Path.GetFullPath(Path.Combine(basePath, filePath));
-        if (!targetPath.StartsWith(basePath))
+        if (!WorkspaceHelper.IsSubPathOf(targetPath, basePath))
         {
             ctx.Response.StatusCode = 403;
             return;
@@ -218,7 +219,7 @@ public static class WorkspaceEndpoint
         }
 
         var targetPath = Path.GetFullPath(Path.Combine(basePath, filePath));
-        if (!targetPath.StartsWith(basePath))
+        if (!WorkspaceHelper.IsSubPathOf(targetPath, basePath))
         {
             ctx.Response.StatusCode = 403;
             return;
@@ -271,7 +272,7 @@ public static class WorkspaceEndpoint
         }
 
         var targetPath = Path.GetFullPath(Path.Combine(basePath, dirPath));
-        if (!targetPath.StartsWith(basePath))
+        if (!WorkspaceHelper.IsSubPathOf(targetPath, basePath))
         {
             ctx.Response.StatusCode = 403;
             return;
@@ -287,7 +288,7 @@ public static class WorkspaceEndpoint
         Directory.CreateDirectory(targetPath);
         await ctx.Response.WriteAsJsonAsync(new
         {
-            path = Path.GetRelativePath(basePath, targetPath).Replace('\\', '/'),
+            path = WorkspaceHelper.GetRelativePath(basePath, targetPath),
             created = true
         });
     }
@@ -296,7 +297,18 @@ public static class WorkspaceEndpoint
 
     private static async Task HandleBrowse(HttpContext ctx)
     {
-        var path = ctx.Request.Query["path"].FirstOrDefault() ?? "/";
+        var path = ctx.Request.Query["path"].FirstOrDefault() ?? (WorkspaceHelper.IsWindows ? "" : "/");
+
+        // Windows: Leerer Pfad oder Root → Laufwerke anzeigen
+        if (WorkspaceHelper.IsWindows && string.IsNullOrEmpty(path))
+        {
+            var drives = System.IO.DriveInfo.GetDrives()
+                .Where(d => d.IsReady)
+                .Select(d => new { name = d.Name.TrimEnd('\\'), path = d.Name.Replace('\\', '/'), type = "dir" })
+                .ToList<object>();
+            await ctx.Response.WriteAsJsonAsync(new { current = "", entries = drives });
+            return;
+        }
 
         var targetPath = Path.GetFullPath(path);
         if (!Directory.Exists(targetPath))
@@ -368,7 +380,7 @@ public static class WorkspaceEndpoint
         if (basePath == null) return;
 
         var targetPath = Path.GetFullPath(Path.Combine(basePath, filePath));
-        if (!targetPath.StartsWith(basePath))
+        if (!WorkspaceHelper.IsSubPathOf(targetPath, basePath))
         {
             ctx.Response.StatusCode = 403;
             return;