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, 41 insertions, 0 deletions

diff --git a/internal/task/story.go b/internal/task/story.go
new file mode 100644
index 0000000..536bda1
--- /dev/null
+++ b/internal/task/story.go
@@ -0,0 +1,41 @@
+package task
+
+import "time"
+
+type StoryState string
+
+const (
+	StoryPending     StoryState = "PENDING"
+	StoryInProgress  StoryState = "IN_PROGRESS"
+	StoryShippable   StoryState = "SHIPPABLE"
+	StoryDeployed    StoryState = "DEPLOYED"
+	StoryValidating  StoryState = "VALIDATING"
+	StoryReviewReady StoryState = "REVIEW_READY"
+	StoryNeedsFix    StoryState = "NEEDS_FIX"
+)
+
+type Story struct {
+	ID             string     `json:"id"`
+	Name           string     `json:"name"`
+	ProjectID      string     `json:"project_id"`
+	BranchName     string     `json:"branch_name"`
+	DeployConfig   string     `json:"deploy_config"`
+	ValidationJSON string     `json:"validation_json"`
+	Status         StoryState `json:"status"`
+	CreatedAt      time.Time  `json:"created_at"`
+	UpdatedAt      time.Time  `json:"updated_at"`
+}
+
+var validStoryTransitions = map[StoryState]map[StoryState]bool{
+	StoryPending:     {StoryInProgress: true},
+	StoryInProgress:  {StoryShippable: true, StoryNeedsFix: true},
+	StoryShippable:   {StoryDeployed: true},
+	StoryDeployed:    {StoryValidating: true},
+	StoryValidating:  {StoryReviewReady: true, StoryNeedsFix: true},
+	StoryReviewReady: {},
+	StoryNeedsFix:    {StoryInProgress: true},
+}
+
+func ValidStoryTransition(from, to StoryState) bool {
+	return validStoryTransitions[from][to]
+}