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/Config/WorkerConfig.cs

@@ -0,0 +1,70 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using ClaudeDo.Data;
+
+namespace ClaudeDo.Worker.Config;
+
+public sealed class WorkerConfig
+{
+    [JsonPropertyName("db_path")]
+    public string DbPath { get; set; } = "~/.todo-app/todo.db";
+
+    [JsonPropertyName("sandbox_root")]
+    public string SandboxRoot { get; set; } = "~/.todo-app/sandbox";
+
+    [JsonPropertyName("log_root")]
+    public string LogRoot { get; set; } = "~/.todo-app/logs";
+
+    /// <summary>"sibling" → place worktrees next to the target repo; "central" → under <see cref="CentralWorktreeRoot"/>.</summary>
+    [JsonPropertyName("worktree_root_strategy")]
+    public string WorktreeRootStrategy { get; set; } = "sibling";
+
+    [JsonPropertyName("central_worktree_root")]
+    public string CentralWorktreeRoot { get; set; } = "~/.todo-app/worktrees";
+
+    [JsonPropertyName("queue_backstop_interval_ms")]
+    public int QueueBackstopIntervalMs { get; set; } = 30_000;
+
+    [JsonPropertyName("signalr_port")]
+    public int SignalRPort { get; set; } = 47_821;
+
+    [JsonPropertyName("claude_bin")]
+    public string ClaudeBin { get; set; } = "claude";
+
+    public static string DefaultConfigPath =>
+        Path.Combine(Paths.AppDataRoot(), "worker.config.json");
+
+    /// <summary>
+    /// Loads the config from <paramref name="path"/> (defaults to <see cref="DefaultConfigPath"/>).
+    /// Missing file → returns defaults. Resolves all path-typed fields to absolute paths.
+    /// </summary>
+    public static WorkerConfig Load(string? path = null)
+    {
+        path ??= DefaultConfigPath;
+
+        WorkerConfig cfg;
+        if (File.Exists(path))
+        {
+            var json = File.ReadAllText(path);
+            cfg = JsonSerializer.Deserialize<WorkerConfig>(json, JsonOpts)
+                ?? throw new InvalidOperationException($"Failed to parse {path}");
+        }
+        else
+        {
+            cfg = new WorkerConfig();
+        }
+
+        cfg.DbPath = Paths.Expand(cfg.DbPath);
+        cfg.SandboxRoot = Paths.Expand(cfg.SandboxRoot);
+        cfg.LogRoot = Paths.Expand(cfg.LogRoot);
+        cfg.CentralWorktreeRoot = Paths.Expand(cfg.CentralWorktreeRoot);
+
+        return cfg;
+    }
+
+    private static readonly JsonSerializerOptions JsonOpts = new()
+    {
+        ReadCommentHandling = JsonCommentHandling.Skip,
+        AllowTrailingCommas = true,
+    };
+}