Implement bd-10: Export/import dependencies in JSONL

Added dependency support to export/import workflow:

Changes:
- Added GetDependencyRecords() to Storage interface to get raw dependency records
- Extended Issue struct with Dependencies field (omitempty for backward compat)
- Modified export.go to populate dependencies for each issue
- Modified import.go to process dependencies in second pass after all issues exist
- All tests pass

Benefits:
- JSONL is now self-contained with full dependency information
- Enables proper collision resolution in future (bd-12+)
- Idempotent imports: existing dependencies are not duplicated
- Forward references handled: dependencies created after all issues exist

Example output:
{
  "id": "bd-10",
  "title": "...",
  "dependencies": [{
    "issue_id": "bd-10",
    "depends_on_id": "bd-9",
    "type": "parent-child",
    "created_at": "...",
    "created_by": "stevey"
  }]
}

Closes bd-10

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

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

internal/storage/sqlite/dependencies.go

@@ -178,6 +178,38 @@ func (s *SQLiteStorage) GetDependents(ctx context.Context, issueID string) ([]*t
 	return scanIssues(rows)
 }
 
+// GetDependencyRecords returns raw dependency records for an issue
+func (s *SQLiteStorage) GetDependencyRecords(ctx context.Context, issueID string) ([]*types.Dependency, error) {
+	rows, err := s.db.QueryContext(ctx, `
+		SELECT issue_id, depends_on_id, type, created_at, created_by
+		FROM dependencies
+		WHERE issue_id = ?
+		ORDER BY created_at ASC
+	`, issueID)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get dependency records: %w", err)
+	}
+	defer rows.Close()
+
+	var deps []*types.Dependency
+	for rows.Next() {
+		var dep types.Dependency
+		err := rows.Scan(
+			&dep.IssueID,
+			&dep.DependsOnID,
+			&dep.Type,
+			&dep.CreatedAt,
+			&dep.CreatedBy,
+		)
+		if err != nil {
+			return nil, fmt.Errorf("failed to scan dependency: %w", err)
+		}
+		deps = append(deps, &dep)
+	}
+
+	return deps, nil
+}
+
 // GetDependencyTree returns the full dependency tree
 func (s *SQLiteStorage) GetDependencyTree(ctx context.Context, issueID string, maxDepth int) ([]*types.TreeNode, error) {
 	if maxDepth <= 0 {