Make the iPhone app iPhone-only

Set TARGETED_DEVICE_FAMILY to 1 for the iOS target — it was universal (1,2) but
isn't an iPad experience, which forced an iPad screenshot requirement at
submission. The Apple Watch app is a separate target (family 4) and is unaffected.
Removes the iPad screenshot set from the listing metadata.

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

CHANGELOG.md

@@ -4,6 +4,9 @@ All notable changes to this project are documented here.
 
 ## June 2026
 
+- Set the iPhone app to iPhone-only (`TARGETED_DEVICE_FAMILY` 1); it was
+  inadvertently universal but isn't an iPad-shaped experience. The Apple Watch app
+  is a separate target and is unaffected.
 - 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