fix(sqlite): handle deleted_at TEXT column scanning properly

The deleted_at column was defined as TEXT in the schema but code was
trying to scan into sql.NullTime. The ncruces/go-sqlite3 driver only
auto-converts TEXT to time.Time for columns declared as DATETIME/DATE/
TIME/TIMESTAMP. For TEXT columns, it returns raw strings which
sql.NullTime.Scan() cannot handle.

Added parseNullableTimeString() helper that manually parses time strings
and changed all deletedAt variables from sql.NullTime to sql.NullString.

Fixes import failure: "sql: Scan error on column index 22, name
deleted_at: unsupported Scan, storing driver.Value type string into
type *time.Time"

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

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

internal/storage/sqlite/ready.go

@@ -170,7 +170,7 @@ func (s *SQLiteStorage) GetStaleIssues(ctx context.Context, filter types.StaleFi
 		var compactedAtCommit sql.NullString
 		var originalSize sql.NullInt64
 		var closeReason sql.NullString
-		var deletedAt sql.NullTime
+		var deletedAt sql.NullString // TEXT column, not DATETIME - must parse manually
 		var deletedBy sql.NullString
 		var deleteReason sql.NullString
 		var originalType sql.NullString
@@ -221,9 +221,7 @@ func (s *SQLiteStorage) GetStaleIssues(ctx context.Context, filter types.StaleFi
 		if closeReason.Valid {
 			issue.CloseReason = closeReason.String
 		}
-		if deletedAt.Valid {
-			issue.DeletedAt = &deletedAt.Time
-		}
+		issue.DeletedAt = parseNullableTimeString(deletedAt)
 		if deletedBy.Valid {
 			issue.DeletedBy = deletedBy.String
 		}