feat(story): add Epic/Story data model + REST CRUD (Phase 7a)

Pure data model + CRUD -- no orchestration behavior yet (that's Phase 7b).
Revives ADR-007's stories concept (adapted; ADR-007 itself was deleted as
"more machinery than the usage pattern needed") while staying lean: reuses
the existing events/projects/task-tree machinery rather than building a
parallel hierarchy.

- internal/story: Epic/Story types. Epic is a loosely-scoped initiative
  (OPEN/CLOSED, no execution semantics). Story is a shippable slice of work
  realized by a task tree rooted at root_task_id; epic_id/project_id/
  root_task_id are loose references (no FK enforcement, matching the
  codebase's existing tolerance for unmatched reference strings like
  tasks.project).
- storage: new epics/stories tables (additive migrations) + CRUD methods.
  Story status is intentionally unvalidated pass-through in this phase --
  no task.ValidTransition-style state machine, since there's no orchestrator
  yet to make transitions meaningful.
- event: 9 new Kind constants for the ceremony this layer will eventually
  drive (epic_proposed, discovery_proposed, framing_decided, groomed,
  prioritized, eval_verdict, arbitration_decided, retro_captured,
  human_accepted) -- defined but nothing emits them yet.
- api: GET/POST /api/epics, GET/PUT /api/epics/{id}, GET /api/epics/{id}/stories,
  GET/POST /api/stories, GET/PUT /api/stories/{id}, and GET
  /api/stories/{id}/task-tree -- BFS walk from root_task_id following both
  parent_task_id children and depends_on-edge dependents (visited-set
  guarded), returning a flat node list for a later UI phase to render as a
  graph. Unauthenticated, matching the existing projects/tasks endpoints'
  posture.

go build/vet/test -race -count=1 all pass, full suite.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V1moSNCJRcP6kykA4tyUSs

1 files changed, 30 insertions, 0 deletions

diff --git a/internal/storage/db.go b/internal/storage/db.go
index d571c2e..8b563a6 100644
--- a/internal/storage/db.go
+++ b/internal/storage/db.go
@@ -154,6 +154,36 @@ func (s *DB) migrate() error {
 			UNIQUE(role, version)
 		)`,
 		`CREATE INDEX IF NOT EXISTS idx_role_configs_role_status ON role_configs(role, status)`,
+		`CREATE TABLE IF NOT EXISTS epics (
+			id TEXT PRIMARY KEY,
+			name TEXT NOT NULL,
+			description TEXT,
+			status TEXT NOT NULL DEFAULT 'OPEN',
+			discovery_source TEXT,
+			created_at DATETIME NOT NULL,
+			updated_at DATETIME NOT NULL
+		)`,
+		`CREATE TABLE IF NOT EXISTS stories (
+			id TEXT PRIMARY KEY,
+			epic_id TEXT,
+			project_id TEXT,
+			name TEXT NOT NULL,
+			branch_name TEXT,
+			status TEXT NOT NULL,
+			discovery_source TEXT,
+			spec TEXT,
+			acceptance_criteria_json TEXT NOT NULL DEFAULT '[]',
+			validation_json TEXT,
+			deploy_config TEXT,
+			priority TEXT,
+			root_task_id TEXT,
+			created_at DATETIME NOT NULL,
+			updated_at DATETIME NOT NULL
+		)`,
+		`CREATE INDEX IF NOT EXISTS idx_epics_status ON epics(status)`,
+		`CREATE INDEX IF NOT EXISTS idx_stories_status ON stories(status)`,
+		`CREATE INDEX IF NOT EXISTS idx_stories_epic_id ON stories(epic_id)`,
+		`CREATE INDEX IF NOT EXISTS idx_stories_root_task_id ON stories(root_task_id)`,
 	}
 	for _, m := range migrations {
 		if _, err := s.db.Exec(m); err != nil {