migrate to the new for-loop syntax

Drop the ':' before captures (for xs (x) / for 0..n (i)); the index
capture becomes the trailing open range (for xs, 0.. (x, i)). 136
headers across 26 files, mechanical.

Five headless tests (banner_layout, hit_test, swipe_commit,
swipe_intent, swipe_reshuffle) also gain a direct
#import "modules/ui/types.sx" — they named Point/Frame through a
transitive import, which bare visibility no longer permits.

Gates: sx build --target ios-sim main.sx links; tools/run_tests.sh
23/23.

gem_anim.sx

@@ -132,7 +132,7 @@ GemMotion :: struct {
     // its resting pose instead of replaying the prior move's landing wobble; the
     // idle clock keeps running, so the always-on idle simply resumes from rest.
     reset_landings :: (self: *GemMotion) {
-        for 0..BOARD_CELLS: (i) { self.land_at[i] = -1000.0; }
+        for 0..BOARD_CELLS (i) { self.land_at[i] = -1000.0; }
     }
 
     stamp_land :: (self: *GemMotion, i: s64) {