Add orphan detection migration (bd-3852)

Creates migration to detect orphaned child issues and logs them for user
action. Orphaned children are issues with hierarchical IDs (e.g., "parent.child")
where the parent issue no longer exists in the database.

The migration:
- Queries for issues with IDs like '%.%' where parent doesn't exist
- Logs detected orphans with suggested actions (delete, convert, or restore)
- Does NOT automatically delete or convert orphans
- Is idempotent and safe to run multiple times

Test coverage:
- Detects orphaned child issues correctly
- Handles clean databases with no orphans
- Verifies idempotency

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/storage/sqlite/migrations_test.go

@@ -502,3 +502,117 @@ func TestMigrateContentHashColumn(t *testing.T) {
 		}
 	})
 }
+
+func TestMigrateOrphanDetection(t *testing.T) {
+	t.Run("detects orphaned child issues", func(t *testing.T) {
+		store, cleanup := setupTestDB(t)
+		defer cleanup()
+		db := store.db
+		ctx := context.Background()
+
+		// Create a parent issue
+		parent := &types.Issue{
+			ID:        "bd-parent",
+			Title:     "Parent Issue",
+			Priority:  1,
+			IssueType: "task",
+			Status:    "open",
+		}
+		if err := store.CreateIssue(ctx, parent, "test"); err != nil {
+			t.Fatalf("failed to create parent issue: %v", err)
+		}
+
+		// Create a valid child issue
+		validChild := &types.Issue{
+			ID:        "bd-parent.1",
+			Title:     "Valid Child",
+			Priority:  1,
+			IssueType: "task",
+			Status:    "open",
+		}
+		if err := store.CreateIssue(ctx, validChild, "test"); err != nil {
+			t.Fatalf("failed to create valid child: %v", err)
+		}
+
+		// Create an orphaned child by directly inserting it into the database
+		// (bypassing CreateIssue validation which checks for parent existence)
+		_, err := db.Exec(`
+			INSERT INTO issues (id, title, status, priority, issue_type, created_at, updated_at)
+			VALUES (?, ?, ?, ?, ?, datetime('now'), datetime('now'))
+		`, "bd-missing.1", "Orphaned Child", "open", 1, "task")
+		if err != nil {
+			t.Fatalf("failed to create orphan: %v", err)
+		}
+
+		// Run migration - it should detect the orphan and log it
+		if err := migrations.MigrateOrphanDetection(db); err != nil {
+			t.Fatalf("failed to run orphan detection migration: %v", err)
+		}
+
+		// Verify the orphan still exists (migration doesn't delete)
+		got, err := store.GetIssue(ctx, "bd-missing.1")
+		if err != nil {
+			t.Fatalf("orphan should still exist after migration: %v", err)
+		}
+		if got.ID != "bd-missing.1" {
+			t.Errorf("expected orphan ID bd-missing.1, got %s", got.ID)
+		}
+
+		// Verify valid child still exists
+		got, err = store.GetIssue(ctx, "bd-parent.1")
+		if err != nil {
+			t.Fatalf("valid child should still exist: %v", err)
+		}
+		if got.ID != "bd-parent.1" {
+			t.Errorf("expected valid child ID bd-parent.1, got %s", got.ID)
+		}
+	})
+
+	t.Run("no orphans found in clean database", func(t *testing.T) {
+		store, cleanup := setupTestDB(t)
+		defer cleanup()
+		db := store.db
+		ctx := context.Background()
+
+		// Create a parent with valid children
+		parent := &types.Issue{
+			ID:        "bd-p1",
+			Title:     "Parent",
+			Priority:  1,
+			IssueType: "task",
+			Status:    "open",
+		}
+		if err := store.CreateIssue(ctx, parent, "test"); err != nil {
+			t.Fatalf("failed to create parent: %v", err)
+		}
+
+		child := &types.Issue{
+			ID:        "bd-p1.1",
+			Title:     "Child",
+			Priority:  1,
+			IssueType: "task",
+			Status:    "open",
+		}
+		if err := store.CreateIssue(ctx, child, "test"); err != nil {
+			t.Fatalf("failed to create child: %v", err)
+		}
+
+		// Run migration - should succeed with no orphans
+		if err := migrations.MigrateOrphanDetection(db); err != nil {
+			t.Fatalf("migration should succeed with clean data: %v", err)
+		}
+	})
+
+	t.Run("is idempotent", func(t *testing.T) {
+		store, cleanup := setupTestDB(t)
+		defer cleanup()
+		db := store.db
+
+		// Run migration multiple times
+		for i := 0; i < 3; i++ {
+			if err := migrations.MigrateOrphanDetection(db); err != nil {
+				t.Fatalf("migration run %d failed: %v", i+1, err)
+			}
+		}
+	})
+}