Add App Store screenshot harness + listing metadata

DEBUG-only screenshot support (seeded sample data via ScreenshotSeed, per-screen
launch args, screenshot roots for both apps) so iPhone + Apple Watch App Store
shots can be captured deterministically from the simulator — all excluded from
release builds. Also seed ExerciseView's set-grid progress in init so it renders
correctly on the first frame. Adds Scripts/metadata/ as the listing source of
truth (copy, URLs, review notes, and the captured screenshots).

Claude-Session: https://claude.ai/code/session_018gg69MaUetDNzWzBXisfMV

CHANGELOG.md

@@ -4,6 +4,12 @@ All notable changes to this project are documented here.
 
 ## June 2026
 
+- Exercise detail now renders the set-progress grid correctly on the first frame
+  (seeded from the log in `init`) instead of filling in a frame later.
+- Added a DEBUG-only screenshot harness (seeded sample data + `--screenshot
+  --screen <name>` launch args, excluded from release builds) for generating App
+  Store screenshots from the iPhone and Apple Watch simulators, plus the
+  `Scripts/metadata/` App Store listing source of truth.
 - Redesigned the Apple Watch app into a focused workout runner: it opens directly
   on the active workout's exercise list (or prompts you to start one on iPhone),
   and each exercise runs as a horizontally-paged HIIT cycle — a count-up work