feat(data,worker): add db schema init and signalr hub skeleton

Data layer: Paths helper with ~/%USERPROFILE% expansion, SqliteConnectionFactory
(WAL + foreign keys), SchemaInitializer that applies the embedded schema.sql, and
POCO entities for lists/tasks/tags/worktrees.

Worker: WorkerConfig loader (~/.todo-app/worker.config.json with defaults),
WorkerHub exposing Ping(), and Program.cs wiring Kestrel to 127.0.0.1:<port>,
SignalR at /hub, schema applied on startup.

Pins Microsoft.Data.Sqlite and Microsoft.Extensions.Hosting to 8.x for net8.0
compatibility.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Worker/Program.cs

@@ -1,6 +1,27 @@
+using ClaudeDo.Data;
+using ClaudeDo.Worker.Config;
+using ClaudeDo.Worker.Hub;
+
+var cfg = WorkerConfig.Load();
+
 var builder = WebApplication.CreateBuilder(args);
+
+// Initialize DB schema before the host starts accepting connections.
+var dbFactory = new SqliteConnectionFactory(cfg.DbPath);
+SchemaInitializer.Apply(dbFactory);
+
+builder.Services.AddSingleton(cfg);
+builder.Services.AddSingleton(dbFactory);
+builder.Services.AddSignalR();
+
+// Loopback-only bind. Firewall is irrelevant for 127.0.0.1.
+builder.WebHost.UseUrls($"http://127.0.0.1:{cfg.SignalRPort}");
+
 var app = builder.Build();
 
-app.MapGet("/", () => "Hello World!");
+app.MapHub<WorkerHub>("/hub");
+
+app.Logger.LogInformation("ClaudeDo.Worker listening on http://127.0.0.1:{Port} (db: {Db})",
+    cfg.SignalRPort, cfg.DbPath);
 
 app.Run();