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/config.go

@@ -0,0 +1,110 @@
+package dolt
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"strings"
+)
+
+// SetConfig sets a configuration value
+func (s *DoltStore) SetConfig(ctx context.Context, key, value string) error {
+	_, err := s.db.ExecContext(ctx, `
+		INSERT INTO config (` + "`key`" + `, value) VALUES (?, ?)
+		ON DUPLICATE KEY UPDATE value = VALUES(value)
+	`, key, value)
+	if err != nil {
+		return fmt.Errorf("failed to set config %s: %w", key, err)
+	}
+	return nil
+}
+
+// GetConfig retrieves a configuration value
+func (s *DoltStore) GetConfig(ctx context.Context, key string) (string, error) {
+	var value string
+	err := s.db.QueryRowContext(ctx, "SELECT value FROM config WHERE `key` = ?", key).Scan(&value)
+	if err == sql.ErrNoRows {
+		return "", nil
+	}
+	if err != nil {
+		return "", fmt.Errorf("failed to get config %s: %w", key, err)
+	}
+	return value, nil
+}
+
+// GetAllConfig retrieves all configuration values
+func (s *DoltStore) GetAllConfig(ctx context.Context) (map[string]string, error) {
+	rows, err := s.db.QueryContext(ctx, "SELECT `key`, value FROM config")
+	if err != nil {
+		return nil, fmt.Errorf("failed to get all config: %w", err)
+	}
+	defer rows.Close()
+
+	config := make(map[string]string)
+	for rows.Next() {
+		var key, value string
+		if err := rows.Scan(&key, &value); err != nil {
+			return nil, fmt.Errorf("failed to scan config: %w", err)
+		}
+		config[key] = value
+	}
+	return config, rows.Err()
+}
+
+// DeleteConfig removes a configuration value
+func (s *DoltStore) DeleteConfig(ctx context.Context, key string) error {
+	_, err := s.db.ExecContext(ctx, "DELETE FROM config WHERE `key` = ?", key)
+	if err != nil {
+		return fmt.Errorf("failed to delete config %s: %w", key, err)
+	}
+	return nil
+}
+
+// SetMetadata sets a metadata value
+func (s *DoltStore) SetMetadata(ctx context.Context, key, value string) error {
+	_, err := s.db.ExecContext(ctx, `
+		INSERT INTO metadata (` + "`key`" + `, value) VALUES (?, ?)
+		ON DUPLICATE KEY UPDATE value = VALUES(value)
+	`, key, value)
+	if err != nil {
+		return fmt.Errorf("failed to set metadata %s: %w", key, err)
+	}
+	return nil
+}
+
+// GetMetadata retrieves a metadata value
+func (s *DoltStore) GetMetadata(ctx context.Context, key string) (string, error) {
+	var value string
+	err := s.db.QueryRowContext(ctx, "SELECT value FROM metadata WHERE `key` = ?", key).Scan(&value)
+	if err == sql.ErrNoRows {
+		return "", nil
+	}
+	if err != nil {
+		return "", fmt.Errorf("failed to get metadata %s: %w", key, err)
+	}
+	return value, nil
+}
+
+// GetCustomStatuses returns custom status values from config
+func (s *DoltStore) GetCustomStatuses(ctx context.Context) ([]string, error) {
+	value, err := s.GetConfig(ctx, "status.custom")
+	if err != nil {
+		return nil, err
+	}
+	if value == "" {
+		return nil, nil
+	}
+	return strings.Split(value, ","), nil
+}
+
+// GetCustomTypes returns custom issue type values from config
+func (s *DoltStore) GetCustomTypes(ctx context.Context) ([]string, error) {
+	value, err := s.GetConfig(ctx, "types.custom")
+	if err != nil {
+		return nil, err
+	}
+	if value == "" {
+		return nil, nil
+	}
+	return strings.Split(value, ","), nil
+}