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.

tests/cascade_cue.sx

@@ -15,7 +15,7 @@ main :: () -> s32 {
     // middle are visible: depths 0,1 pin to the first cue; depths >= 5 pin to
     // the last; 2,3,4 step up one cue at a time.
     prev : s64 = -1;
-    for 0..10: (depth) {
+    for 0..10 (depth) {
         idx := cascade_cue_index(depth);
         print("depth {} -> idx {} ({})\n", depth, idx, cascade_cue_name(idx));
         // The mapping must never step down as depth grows.