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.

Workouts/Views/Splits/SplitAddEditView.swift

@@ -7,6 +7,7 @@
 // Copyright 2025 Rouslan Zenetl. All Rights Reserved.
 //
 
+import IndieSync
 import SwiftUI
 import SwiftData
 
@@ -157,7 +158,7 @@ struct SplitAddEditView: View {
             // Create new split
             let existing = (try? modelContext.fetch(FetchDescriptor<Split>())) ?? []
             let doc = SplitDocument(
-                schemaVersion: SplitDocument.currentSchema,
+                schemaVersion: SplitDocument.currentSchemaVersion,
                 id: ULID.make(),
                 name: name,
                 color: color,