feat(worker): map MCP HTTP endpoint and broadcast TaskUpdated

- Add PlanningMcpContextAccessor (Option A) to read PlanningMcpContext
  from HttpContext.Items set by PlanningTokenAuthMiddleware
- Annotate PlanningMcpService with [McpServerToolType]/[McpServerTool]
  and remove PlanningMcpContext ctx parameter from all tool methods
- Broadcast TaskUpdated(parentTaskId) via HubBroadcaster after every
  mutation in PlanningMcpService
- Refactor PlanningSessionManager to accept IDbContextFactory for
  singleton-safe use in DI; keep direct-repo ctor for tests
- Register PlanningSessionManager (singleton), IPlanningTerminalLauncher,
  PlanningMcpContextAccessor, PlanningMcpService, and MCP server in
  Program.cs; wire PlanningTokenAuthMiddleware and MapMcp("/mcp")
- Update PlanningMcpServiceTests with fake HttpContext accessor and
  no-op HubBroadcaster (avoids Moq dependency)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Worker/Planning/PlanningMcpContextAccessor.cs

@@ -0,0 +1,14 @@
+using Microsoft.AspNetCore.Http;
+
+namespace ClaudeDo.Worker.Planning;
+
+public sealed class PlanningMcpContextAccessor
+{
+    private readonly IHttpContextAccessor _http;
+
+    public PlanningMcpContextAccessor(IHttpContextAccessor http) => _http = http;
+
+    public PlanningMcpContext Current =>
+        (_http.HttpContext?.Items["PlanningContext"] as PlanningMcpContext)
+        ?? throw new InvalidOperationException("No planning context on request.");
+}