feat(sync): préparation à la synchronisation cloud (ticket #12)

Ajuste les ports et le bootstrap applicatif, ainsi que le mapping
Drift des repositories, pour préparer une future synchronisation cloud
(invariants documentés dans docs/sync-invariants.md). Corrige au
passage un bug de fuseau horaire UTC dans le mapping Drift. flutter
analyze propre, 35/35 tests verts, build APK debug validé.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/sync-invariants.md

@@ -0,0 +1,34 @@
+# Sync invariants
+
+GameTime remains offline-first. The current sync surface is preparatory only:
+there is no server protocol, remote auth, or network adapter yet.
+
+## Local mutation log
+
+Every local mutation of a syncable aggregate must update the row metadata and
+append a `change_log` entry in the same local transaction.
+
+Required row metadata:
+- `id` is stable and generated locally.
+- `updatedAt` is the logical mutation timestamp.
+- `syncState` is `dirty` for local writes and `deleted` for soft deletes.
+- `localRevision` increases when an existing row changes.
+- `originDeviceId` identifies the device that produced the row mutation.
+- `futureOwnerProfileId` is nullable until user profiles exist.
+
+`change_log.operation` currently supports `insert`, `update`, `softDelete`, and
+`restore`. Exercise archive/unarchive is represented as `update` because the row
+is not deleted and the current schema has no `archive` operation.
+
+## Future conflict policy
+
+Conflict resolution is not implemented yet. The intended first server strategy is
+last-write-wins per entity using `updatedAt`, with `localRevision` and
+`originDeviceId` retained for diagnostics and later upgrade. Vector clocks are not
+implemented and are not assumed by the current model.
+
+## Future profiles
+
+The profile boundary will attach to `futureOwnerProfileId`. Until profile support
+is added, rows keep it nullable and sync code must not infer ownership from local
+device IDs.