Wire Marvin tasks adapter into the daemon

main constructs the Marvin adapter (command overridable via
ANTIDRIFT_MARVIN_CMD) and injects it. Adds a web test asserting the
planning state payload carries today's tasks.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/web/web_test.go

@@ -13,6 +13,7 @@ import (
 	"antidrift/internal/domain"
 	"antidrift/internal/evidence"
 	"antidrift/internal/session"
+	"antidrift/internal/tasks"
 
 	"github.com/gin-gonic/gin"
 )
@@ -230,6 +231,37 @@ func TestServesStaticAssets(t *testing.T) {
 	}
 }
 
+type stubProvider struct {
+	list []tasks.Task
+}
+
+func (s stubProvider) Today(ctx context.Context) ([]tasks.Task, error) {
+	return s.list, nil
+}
+
+func TestPlanningStatePayloadCarriesTasks(t *testing.T) {
+	s := newTestServer(t)
+	s.ctrl.SetTasks(stubProvider{list: []tasks.Task{{ID: "a", Title: "Write the spec", Day: "2026-05-31"}}})
+	r := s.Router()
+	if w := post(t, r, "/planning", ""); w.Code != http.StatusOK {
+		t.Fatalf("/planning code %d", w.Code)
+	}
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		if tv := s.ctrl.State().Tasks; tv != nil && tv.Status == "ready" {
+			break
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
+	js := s.stateJSON()
+	if !strings.Contains(js, `"tasks"`) {
+		t.Fatalf("planning payload missing tasks object: %s", js)
+	}
+	if !strings.Contains(js, `"title":"Write the spec"`) {
+		t.Fatalf("planning payload missing task title: %s", js)
+	}
+}
+
 func TestCommitmentCarriesAllowedClassesAndRoutesWork(t *testing.T) {
 	s := newTestServer(t)
 	r := s.Router()