fix(memory): 定宽时间戳存储 + rowid 确定性排序 + 遗留数据归一化

- formatTime 改用固定 30 字节布局(9 位小数秒)，让 TEXT 列的字典序与时间序一致（RFC3339Nano 会去掉尾随零产生变宽字符串，秒内会反序）
- memory_items / project / project_chapter 的 ORDER BY 全部补 rowid 兜底，消除同 tick 打平时的顺序不确定
- 开库时幂等归一化变宽的历史值；无法解析的行原样保留，不阻塞开库
- 回归测试：变宽排序反例、同一时间戳插入序、归一化幂等与跳过

internal/runtime/memory/projectindex/project.go

@@ -142,21 +142,3 @@ func newID() (string, error) {
 	}
 	return hex.EncodeToString(b), nil
 }
-
-// formatTime encodes t in UTC as an RFC3339Nano string so ordering and
-// round-trips are stable across processes.
-func formatTime(t time.Time) string {
-	return t.UTC().Format(time.RFC3339Nano)
-}
-
-// parseTime decodes a stored RFC3339 string; blank input yields a zero time.
-func parseTime(s string) (time.Time, error) {
-	if strings.TrimSpace(s) == "" {
-		return time.Time{}, nil
-	}
-	t, err := time.Parse(time.RFC3339Nano, s)
-	if err != nil {
-		return time.Time{}, fmt.Errorf("projectindex: parse time %q: %w", s, err)
-	}
-	return t, nil
-}