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.

project.yml

@@ -19,6 +19,9 @@ packages:
   IndieAbout:
     url: https://git.rzen.dev/rzen/indie-about.git
     from: "0.2.2"
+  IndieSync:
+    url: https://git.rzen.dev/rzen/indie-sync.git
+    from: "0.1.0"
   Yams:
     url: https://github.com/jpsim/Yams
     from: "6.0.0"
@@ -45,6 +48,7 @@ targets:
         type: file
     dependencies:
       - package: IndieAbout
+      - package: IndieSync
       - package: Yams
       - target: Workouts Watch App
     postBuildScripts:
@@ -81,6 +85,7 @@ targets:
           - "Resources/Info-*.plist"
           - "Resources/*.entitlements"
     dependencies:
+      - package: IndieSync
       - target: Workouts Watch Widget
         embed: true
     postBuildScripts: