Per-session workspace, tools only when workspace set

- Session has workspace field (absolute path, optional)
- ToolService stateless, receives workspace per call
- No workspace = no tools sent to API
- Removed hardcoded workspace from Program.cs
- Workspace field in session edit form

Program.cs

@@ -9,10 +9,8 @@ var builder = WebApplication.CreateBuilder(args);
 builder.Services.AddHttpClient();
 
 var dataDir = Path.Combine(AppContext.BaseDirectory, "data");
-var workspaceRoot = Path.Combine(dataDir, "workspace");
-Directory.CreateDirectory(workspaceRoot);
 
-builder.Services.AddSingleton(new ToolService(workspaceRoot));
+builder.Services.AddSingleton(new ToolService());
 builder.Services.AddSingleton(new DatabaseService(Path.Combine(dataDir, "gott.db")));
 
 var app = builder.Build();