Seed machine-based starter routine from screenshots

Replace the bodyweight-catalog-derived seed (hardcoded 3x10, weight 0) with an
explicit curated machine-based routine: Upper Body, Core, and Lower Body at 4x10
with starting weights taken from real workout logs. Decoupled from the shared
exercise catalog YAML (still used by the exercise picker).

CHANGELOG.md

@@ -14,8 +14,8 @@ All notable changes to this project are documented here.
   ULIDs (the phone is the sole writer of iCloud Drive).
 - Migrated the project to XcodeGen; iOS 26 / watchOS 26, Swift 6 strict
   concurrency.
-- Splits ship as on-demand starter data generated from the bundled exercise
-  catalogs.
+- Splits ship as an on-demand machine-based starter routine (Upper Body, Core,
+  Lower Body) at 4×10 with sensible starting weights.
 - Stored exercise/log durations as integer seconds (was a `Date` epoch hack).
 - Fixed: workout marked complete on creation, an undismissable delete dialog,
   toolbar buttons hidden by nested navigation stacks, and a placeholder