feat: Phase 3 — stories data model, ValidStoryTransition, storage CRUD, API endpoints

- internal/task/story.go: Story struct, StoryState constants, ValidStoryTransition
- internal/task/task.go: add StoryID field
- internal/storage/db.go: stories table + story_id on tasks migrations; CreateStory,
  GetStory, ListStories, UpdateStoryStatus, ListTasksByStory; update all task
  SELECT/INSERT to include story_id; scanTask extended with sql.NullString for story_id;
  added modernc timestamp format to GetMaxUpdatedAt
- internal/storage/sqlite_cgo.go + sqlite_nocgo.go: build-tag based driver selection
  (mattn/go-sqlite3 with CGO, modernc.org/sqlite pure-Go fallback) so tests run
  without a C compiler
- internal/api/stories.go: GET/POST /api/stories, GET /api/stories/{id},
  GET/POST /api/stories/{id}/tasks (auto-wires depends_on chain),
  PUT /api/stories/{id}/status (validates transition)
- internal/api/server.go: register all story routes
- go.mod/go.sum: add modernc.org/sqlite pure-Go dependency

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

1 files changed, 114 insertions, 0 deletions

diff --git a/internal/storage/db_test.go b/internal/storage/db_test.go
index 82c8262..0426bd0 100644
--- a/internal/storage/db_test.go
+++ b/internal/storage/db_test.go
@@ -1218,3 +1218,117 @@ func TestUpdateProject(t *testing.T) {
 	}
 }
 
+func TestCreateStory(t *testing.T) {
+	db := testDB(t)
+	st := &task.Story{
+		ID:     "story-1",
+		Name:   "My Story",
+		Status: task.StoryPending,
+	}
+	if err := db.CreateStory(st); err != nil {
+		t.Fatalf("CreateStory: %v", err)
+	}
+}
+
+func TestGetStory(t *testing.T) {
+	db := testDB(t)
+	st := &task.Story{
+		ID:        "story-2",
+		Name:      "Get Story",
+		ProjectID: "proj-1",
+		Status:    task.StoryPending,
+	}
+	if err := db.CreateStory(st); err != nil {
+		t.Fatalf("CreateStory: %v", err)
+	}
+	got, err := db.GetStory("story-2")
+	if err != nil {
+		t.Fatalf("GetStory: %v", err)
+	}
+	if got.Name != "Get Story" {
+		t.Errorf("Name: want 'Get Story', got %q", got.Name)
+	}
+	if got.ProjectID != "proj-1" {
+		t.Errorf("ProjectID: want 'proj-1', got %q", got.ProjectID)
+	}
+	if got.Status != task.StoryPending {
+		t.Errorf("Status: want PENDING, got %q", got.Status)
+	}
+}
+
+func TestListStories(t *testing.T) {
+	db := testDB(t)
+	for _, name := range []string{"A", "B", "C"} {
+		if err := db.CreateStory(&task.Story{ID: name, Name: name, Status: task.StoryPending}); err != nil {
+			t.Fatalf("CreateStory %s: %v", name, err)
+		}
+	}
+	stories, err := db.ListStories()
+	if err != nil {
+		t.Fatalf("ListStories: %v", err)
+	}
+	if len(stories) != 3 {
+		t.Errorf("want 3 stories, got %d", len(stories))
+	}
+}
+
+func TestUpdateStoryStatus(t *testing.T) {
+	db := testDB(t)
+	st := &task.Story{ID: "story-upd", Name: "Upd", Status: task.StoryPending}
+	if err := db.CreateStory(st); err != nil {
+		t.Fatalf("CreateStory: %v", err)
+	}
+	if err := db.UpdateStoryStatus("story-upd", task.StoryInProgress); err != nil {
+		t.Fatalf("UpdateStoryStatus: %v", err)
+	}
+	got, _ := db.GetStory("story-upd")
+	if got.Status != task.StoryInProgress {
+		t.Errorf("Status: want IN_PROGRESS, got %q", got.Status)
+	}
+}
+
+func TestListTasksByStory(t *testing.T) {
+	db := testDB(t)
+	now := time.Now().UTC()
+
+	if err := db.CreateStory(&task.Story{ID: "story-tasks", Name: "S", Status: task.StoryPending}); err != nil {
+		t.Fatalf("CreateStory: %v", err)
+	}
+
+	makeTask := func(id string) *task.Task {
+		return &task.Task{
+			ID:        id,
+			Name:      id,
+			StoryID:   "story-tasks",
+			Agent:     task.AgentConfig{Type: "claude"},
+			Priority:  task.PriorityNormal,
+			Tags:      []string{},
+			DependsOn: []string{},
+			Retry:     task.RetryConfig{MaxAttempts: 1},
+			State:     task.StatePending,
+			CreatedAt: now,
+			UpdatedAt: now,
+		}
+	}
+
+	if err := db.CreateTask(makeTask("t1")); err != nil {
+		t.Fatal(err)
+	}
+	if err := db.CreateTask(makeTask("t2")); err != nil {
+		t.Fatal(err)
+	}
+
+	tasks, err := db.ListTasksByStory("story-tasks")
+	if err != nil {
+		t.Fatalf("ListTasksByStory: %v", err)
+	}
+	if len(tasks) != 2 {
+		t.Errorf("want 2 tasks, got %d", len(tasks))
+	}
+	for _, tk := range tasks {
+		if tk.StoryID != "story-tasks" {
+			t.Errorf("task %s: StoryID want 'story-tasks', got %q", tk.ID, tk.StoryID)
+		}
+	}
+}
+