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/Hub/WorkerHub.cs

@@ -0,0 +1,16 @@
+using System.Reflection;
+using Microsoft.AspNetCore.SignalR;
+
+namespace ClaudeDo.Worker.Hub;
+
+/// <summary>
+/// SignalR hub the UI connects to. Only <see cref="Ping"/> is implemented at this stage;
+/// RunNow/CancelTask/WakeQueue/GetActive land here once QueueService exists.
+/// </summary>
+public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
+{
+    private static readonly string Version =
+        Assembly.GetExecutingAssembly().GetName().Version?.ToString(3) ?? "0.0.0";
+
+    public string Ping() => $"pong v{Version}";
+}