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/store.go

@@ -79,7 +79,8 @@ type rowScanner interface {
 // internal/db). A nil db returns ErrNilDB. log may be nil, in which case a
 // discard logger is used; the active logger is tagged with source
 // "memory/projectindex" so every record is traceable. ctx controls schema
-// creation and must be honored by the caller.
+// creation and must be honored by the caller. Legacy variable-width timestamps
+// are normalized in place (see normalizeTimestamps).
 func New(ctx context.Context, db *sql.DB, log *slog.Logger) (*Store, error) {
 	if db == nil {
 		return nil, ErrNilDB
@@ -94,6 +95,9 @@ func New(ctx context.Context, db *sql.DB, log *slog.Logger) (*Store, error) {
 			return nil, fmt.Errorf("projectindex: apply schema: %w", err)
 		}
 	}
+	if err := normalizeTimestamps(ctx, db); err != nil {
+		return nil, err
+	}
 	return &Store{db: db, log: log}, nil
 }
 
@@ -106,12 +110,14 @@ func discardLogger(log *slog.Logger) *slog.Logger {
 }
 
 // ListProjects returns every project index entry in insertion order (created_at
-// ASC, id ASC). An empty (non-nil) slice is returned when there are none, so
-// callers can range over it unconditionally. A read error is wrapped with %w so
-// callers can use errors.Is against the package sentinels.
+// ASC, rowid ASC) — rowid breaks created_at ties so projects written within the
+// same clock tick keep their insertion order. An empty (non-nil) slice is
+// returned when there are none, so callers can range over it unconditionally. A
+// read error is wrapped with %w so callers can use errors.Is against the package
+// sentinels.
 func (s *Store) ListProjects(ctx context.Context) ([]Project, error) {
 	rows, err := s.db.QueryContext(ctx, `SELECT id, title, desc, created_at, updated_at
-		FROM project ORDER BY created_at ASC, id ASC`)
+		FROM project ORDER BY created_at ASC, rowid ASC`)
 	if err != nil {
 		return nil, fmt.Errorf("projectindex: list projects: %w", err)
 	}