feat(storage): add Dolt backend for version-controlled issue storage

Implements a complete Dolt storage backend that mirrors the SQLite implementation
with MySQL-compatible syntax and adds version control capabilities.

Key features:
- Full Storage interface implementation (~50 methods)
- Version control operations: commit, push, pull, branch, merge, checkout
- History queries via AS OF and dolt_history_* tables
- Cell-level merge instead of line-level JSONL merge
- SQL injection protection with input validation

Bug fixes applied during implementation:
- Added missing quality_score, work_type, source_system to scanIssue
- Fixed Status() to properly parse boolean staged column
- Added validation to CreateIssues (was missing in batch create)
- Made RenameDependencyPrefix transactional
- Expanded GetIssueHistory to return more complete data

Test coverage: 17 tests covering CRUD, dependencies, labels, search,
comments, events, statistics, and SQL injection protection.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/storage/dolt/dirty.go

@@ -0,0 +1,108 @@
+package dolt
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"time"
+)
+
+// GetDirtyIssues returns IDs of issues that have been modified since last export
+func (s *DoltStore) GetDirtyIssues(ctx context.Context) ([]string, error) {
+	rows, err := s.db.QueryContext(ctx, `
+		SELECT issue_id FROM dirty_issues ORDER BY marked_at ASC
+	`)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get dirty issues: %w", err)
+	}
+	defer rows.Close()
+
+	var ids []string
+	for rows.Next() {
+		var id string
+		if err := rows.Scan(&id); err != nil {
+			return nil, fmt.Errorf("failed to scan issue id: %w", err)
+		}
+		ids = append(ids, id)
+	}
+	return ids, rows.Err()
+}
+
+// GetDirtyIssueHash returns the dirty hash for a specific issue
+func (s *DoltStore) GetDirtyIssueHash(ctx context.Context, issueID string) (string, error) {
+	var hash string
+	err := s.db.QueryRowContext(ctx, `
+		SELECT i.content_hash FROM issues i
+		JOIN dirty_issues d ON i.id = d.issue_id
+		WHERE d.issue_id = ?
+	`, issueID).Scan(&hash)
+	if err != nil {
+		return "", fmt.Errorf("failed to get dirty issue hash: %w", err)
+	}
+	return hash, nil
+}
+
+// ClearDirtyIssuesByID removes specific issues from the dirty list
+func (s *DoltStore) ClearDirtyIssuesByID(ctx context.Context, issueIDs []string) error {
+	if len(issueIDs) == 0 {
+		return nil
+	}
+
+	placeholders := make([]string, len(issueIDs))
+	args := make([]interface{}, len(issueIDs))
+	for i, id := range issueIDs {
+		placeholders[i] = "?"
+		args[i] = id
+	}
+
+	query := fmt.Sprintf("DELETE FROM dirty_issues WHERE issue_id IN (%s)", strings.Join(placeholders, ","))
+	_, err := s.db.ExecContext(ctx, query, args...)
+	if err != nil {
+		return fmt.Errorf("failed to clear dirty issues: %w", err)
+	}
+	return nil
+}
+
+// GetExportHash returns the last export hash for an issue
+func (s *DoltStore) GetExportHash(ctx context.Context, issueID string) (string, error) {
+	var hash string
+	err := s.db.QueryRowContext(ctx, `
+		SELECT content_hash FROM export_hashes WHERE issue_id = ?
+	`, issueID).Scan(&hash)
+	if err != nil {
+		return "", nil // Not found is OK
+	}
+	return hash, nil
+}
+
+// SetExportHash stores the export hash for an issue
+func (s *DoltStore) SetExportHash(ctx context.Context, issueID, contentHash string) error {
+	_, err := s.db.ExecContext(ctx, `
+		INSERT INTO export_hashes (issue_id, content_hash, exported_at)
+		VALUES (?, ?, ?)
+		ON DUPLICATE KEY UPDATE content_hash = VALUES(content_hash), exported_at = VALUES(exported_at)
+	`, issueID, contentHash, time.Now())
+	if err != nil {
+		return fmt.Errorf("failed to set export hash: %w", err)
+	}
+	return nil
+}
+
+// ClearAllExportHashes removes all export hashes (for full re-export)
+func (s *DoltStore) ClearAllExportHashes(ctx context.Context) error {
+	_, err := s.db.ExecContext(ctx, "DELETE FROM export_hashes")
+	if err != nil {
+		return fmt.Errorf("failed to clear export hashes: %w", err)
+	}
+	return nil
+}
+
+// GetJSONLFileHash returns the stored JSONL file hash
+func (s *DoltStore) GetJSONLFileHash(ctx context.Context) (string, error) {
+	return s.GetMetadata(ctx, "jsonl_file_hash")
+}
+
+// SetJSONLFileHash stores the JSONL file hash
+func (s *DoltStore) SetJSONLFileHash(ctx context.Context, fileHash string) error {
+	return s.SetMetadata(ctx, "jsonl_file_hash", fileHash)
+}