fix(log): bdrive log reads as a timeline — newest first by edit time (#BEA-40) (#90)

`bdrive log` sorted by the lamport clock, so the wall-clock stamps it prints
came out non-monotonic — two 06:09:24 rows above a 06:10:00 row. And every op
of one scan is stamped with that scan's commit time, so a 22-file agent run
collapsed onto a single stamp. Neither is readable as a timeline, which is the
whole job of the command.

Two display-only changes:

- `journal.Op` gains `Mtime` (`omitzero`, so old journals and old binaries are
  unaffected), populated on put ops from the `os.FileInfo` the scan already
  holds. Deletes and conflict copies keep their commit time.
- `syncer.DisplayTime` / `SortForDisplay` order by the timestamp that is
  actually printed, ties broken by reversed `journal.Less`. `bdrive log` sorts
  and *then* truncates, so `-n 25` is the 25 newest by that stamp.

`journal.Less`, `Sort`, and `Replay` are untouched — replay order is the
convergence contract, so the sort lives in `syncer`, not in `journal`.
`LogEntries` also keeps returning causal order because `bdrive restore` walks
it to find a file's previous version.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

architecture/cli-sync.md

@@ -24,6 +24,7 @@ classDiagram
         +Cycle(ctx) Result
         +Restore(ctx, path, sha) error
     }
+    note for Session "syncer also exposes LogEntries (causal order, what bdrive restore walks) plus DisplayTime / SortForDisplay — the newest-first-by-clock order bdrive log prints"
     note for Session "Restore writes a historical blob back into the working folder as an ordinary edit (fetching it from the hub when this device never held it) — the next Cycle journals it like any other change; it takes no lock and appends to no journal itself"
     note for Session "internal/syncer — scan → commit local ops → pull peer journals → preserve conflicts → refresh rules → prune → materialize → push blobs then own journal"
     note for Session "Prune (bdrive forget / sync --prune, never the daemon) journals a delete for every replayed path the SHARED ignore rules exclude — the include scope is per-device and must never prune it"
@@ -76,8 +77,9 @@ classDiagram
         +Author +User +UserName
         +Kind put or delete
         +Path +Blob +Size +Mode +Note
+        +Mtime when the file was written
     }
-    note for Op "internal/journal — Less orders by (lamport, time, device, seq); Replay folds to LWW-per-path state; each device writes only its own journal"
+    note for Op "internal/journal — Less orders by (lamport, time, device, seq); Replay folds to LWW-per-path state; each device writes only its own journal. Mtime is display-only (bdrive log shows it, falling back to Time) and never feeds Less or Replay"
 
     class Backend {
         <<interface>>