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/swipe_commit.sx

@@ -13,6 +13,7 @@
 // its trace.sx pulls in a second `Frame` that collides with the UI one. Failure
 // is signalled via a non-zero exit code (the runner checks exit code AND stdout).
 #import "modules/std.sx";
+#import "modules/ui/types.sx";
 #import "board.sx";
 #import "board_layout.sx";
 #import "swipe.sx";
@@ -25,7 +26,7 @@ cell_center :: (lay: *BoardLayout, col: s64, row: s64) -> Point {
 }
 
 boards_equal :: (x: *Board, y: *Board) -> bool {
-    for 0..BOARD_CELLS: (i) {
+    for 0..BOARD_CELLS (i) {
         if !(x.cells[i] == y.cells[i]) { return false; }
     }
     true