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.Data/SchemaInitializer.cs

@@ -0,0 +1,41 @@
+using System.Reflection;
+using Microsoft.Data.Sqlite;
+
+namespace ClaudeDo.Data;
+
+/// <summary>
+/// Applies the embedded schema.sql script. Safe to call on every start — the script uses
+/// IF NOT EXISTS / INSERT OR IGNORE.
+/// </summary>
+public static class SchemaInitializer
+{
+    private const string ResourceName = "ClaudeDo.Data.schema.sql";
+
+    public static void Apply(SqliteConnectionFactory factory)
+    {
+        using var conn = factory.Open();
+        ApplyTo(conn);
+    }
+
+    public static void ApplyTo(SqliteConnection conn)
+    {
+        var sql = LoadScript();
+        using var tx = conn.BeginTransaction();
+        using var cmd = conn.CreateCommand();
+        cmd.Transaction = tx;
+        cmd.CommandText = sql;
+        cmd.ExecuteNonQuery();
+        tx.Commit();
+    }
+
+    private static string LoadScript()
+    {
+        var asm = typeof(SchemaInitializer).Assembly;
+        using var stream = asm.GetManifestResourceStream(ResourceName)
+            ?? throw new InvalidOperationException(
+                $"Embedded resource '{ResourceName}' not found in {asm.GetName().Name}. " +
+                $"Available: {string.Join(", ", asm.GetManifestResourceNames())}");
+        using var reader = new StreamReader(stream);
+        return reader.ReadToEnd();
+    }
+}