Migrate the sync file layer onto the IndieSync package

Replaces the app-local copies of the extracted storage core with the
IndieSync 0.1.0 package (pinned from the new tag): ICloudFileManager ->
DocumentFileStore + TombstoneStore, ICloudFileMonitor ->
MetadataObserver (batched events with the content-date churn gate),
and the shared ULID / DocumentCoder / Tombstone / VersionedDocument
pieces. SyncEngine stays app-specific and is rewired onto the package
types; documents rename currentSchema -> currentSchemaVersion to adopt
the package protocol. ULID.make() remains as a shim minting the string
form the app keys on.

Behavior-preserving: identical JSON bytes (same coder config), same
stub wire format (kind encodes as the same strings), same soft-delete
ordering, same 30-day prune. WorkoutDocument keeps its local-calendar
month bucketing rather than adopting TimeBucketedLayout's UTC paths --
changing derivation would strand existing files. The watch target
links the package too (ULID + DocumentCoder via Shared); iOS, watchOS,
and widget targets all build.

Shared/Model/Mappers.swift

@@ -24,7 +24,7 @@ extension ExerciseDocument {
 
 extension SplitDocument {
     init(from split: Split) {
-        self.init(schemaVersion: Self.currentSchema, id: split.id, name: split.name,
+        self.init(schemaVersion: Self.currentSchemaVersion, id: split.id, name: split.name,
                   color: split.color, systemImage: split.systemImage, order: split.order,
                   createdAt: split.createdAt, updatedAt: split.updatedAt,
                   exercises: split.exercisesArray.map(ExerciseDocument.init(from:)),
@@ -43,7 +43,7 @@ extension WorkoutLogDocument {
 
 extension WorkoutDocument {
     init(from workout: Workout) {
-        self.init(schemaVersion: Self.currentSchema, id: workout.id, splitID: workout.splitID,
+        self.init(schemaVersion: Self.currentSchemaVersion, id: workout.id, splitID: workout.splitID,
                   splitName: workout.splitName, start: workout.start, end: workout.end,
                   status: workout.statusRaw, createdAt: workout.createdAt, updatedAt: workout.updatedAt,
                   logs: workout.logsArray.map(WorkoutLogDocument.init(from:)),