fix(dolt): parse timestamps from TEXT columns instead of direct time.Time scan

The Dolt storage was scanning created_at and updated_at directly into
time.Time fields, but SQLite stores these as TEXT strings. The Go SQLite
driver cannot automatically convert TEXT to time.Time.

Added parseTimeString() helper and fixed all scan functions:
- issues.go: scanIssue()
- dependencies.go: scanIssueRow()
- history.go: GetIssueHistory(), GetIssueAsOf()
- transaction.go: scanIssueTx()

Fixes bd-4dqmy

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

internal/storage/dolt/util.go

@@ -0,0 +1,38 @@
+package dolt
+
+import (
+	"database/sql"
+	"time"
+)
+
+// parseTimeString parses a time string from database TEXT columns (non-nullable).
+// Used for required timestamp fields like created_at/updated_at when stored as TEXT.
+// Returns zero time if parsing fails, which maintains backwards compatibility.
+func parseTimeString(s string) time.Time {
+	if s == "" {
+		return time.Time{}
+	}
+	// Try RFC3339Nano first (more precise), then RFC3339, then SQLite format
+	for _, layout := range []string{time.RFC3339Nano, time.RFC3339, "2006-01-02 15:04:05"} {
+		if t, err := time.Parse(layout, s); err == nil {
+			return t
+		}
+	}
+	return time.Time{} // Unparseable - shouldn't happen with valid data
+}
+
+// parseNullableTimeString parses a nullable time string from database TEXT columns.
+// For columns declared as TEXT (not DATETIME), we must parse manually.
+// Supports RFC3339, RFC3339Nano, and SQLite's native format.
+func parseNullableTimeString(ns sql.NullString) *time.Time {
+	if !ns.Valid || ns.String == "" {
+		return nil
+	}
+	// Try RFC3339Nano first (more precise), then RFC3339, then SQLite format
+	for _, layout := range []string{time.RFC3339Nano, time.RFC3339, "2006-01-02 15:04:05"} {
+		if t, err := time.Parse(layout, ns.String); err == nil {
+			return &t
+		}
+	}
+	return nil // Unparseable - shouldn't happen with valid data
+}