Seed starter splits deterministically with immutable clone-on-edit seeds

Starter splits ship as byte-canonical SplitDocument JSON with fixed
ULIDs (Workouts/Resources/StarterSplits, regenerated by
Scripts/generate_starter_splits.swift) and auto-seed after connect into
a verifiably empty container, re-checked after a settle delay — wrong
guesses are harmless because identical bytes make same-path conflicts
empty and tombstones reap resurrected seeds. Seeds are immutable:
SyncEngine.save(split:) forks an edited seed to a fresh ULID and
soft-deletes the original, whose stub is exempt from pruning
(IndieSync 0.3.0 prune(exempting:)) and vetoes resurrection forever;
split views resolve by id through a redirect map to follow the swap.
Add Starter Splits in Settings restores deleted seeds by lifting the
veto stub and rewriting the bundle bytes.

Also fixes ingestFromWatch bypassing the tombstone veto (a phone-deleted
workout resurrected when a stale watch resent it) and reaps a live file
immediately when its tombstone arrives.

SplitDetailView also picks up the category-grouped exercise sections
from the exercise-category work.

Workouts/Resources/StarterSplits/Core.split.json

@@ -0,0 +1,37 @@
+{
+  "activityType" : 3,
+  "color" : "orange",
+  "createdAt" : "2020-01-01T00:00:00Z",
+  "exercises" : [
+    {
+      "category" : 0,
+      "durationSeconds" : 0,
+      "id" : "01DXF6DT00C4K0NY1NRCFPB3XY",
+      "loadType" : 1,
+      "name" : "Abdominal",
+      "order" : 0,
+      "reps" : 10,
+      "sets" : 4,
+      "weight" : 0,
+      "weightReminderWeeks" : 2
+    },
+    {
+      "category" : 0,
+      "durationSeconds" : 0,
+      "id" : "01DXF6DT001AY3SXTEYHA94MHZ",
+      "loadType" : 1,
+      "name" : "Rotary",
+      "order" : 1,
+      "reps" : 10,
+      "sets" : 4,
+      "weight" : 0,
+      "weightReminderWeeks" : 2
+    }
+  ],
+  "id" : "01DXF6DT001MA0TM7FHJZT098Z",
+  "name" : "Core",
+  "order" : 1,
+  "schemaVersion" : 1,
+  "systemImage" : "figure.core.training",
+  "updatedAt" : "2020-01-01T00:00:00Z"
+}