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/board_init.sx

@@ -12,14 +12,14 @@ SEED :: 1337;
 // independently of the placement logic, so it's a real check, not a tautology.
 count_three_runs :: (b: *Board) -> s32 {
     runs : s32 = 0;
-    for 0..BOARD_ROWS: (row) {
-        for 0..(BOARD_COLS - 2): (col) {
+    for 0..BOARD_ROWS (row) {
+        for 0..(BOARD_COLS - 2) (col) {
             g := b.at(col, row);
             if g == b.at(col + 1, row) and g == b.at(col + 2, row) { runs += 1; }
         }
     }
-    for 0..(BOARD_ROWS - 2): (row) {
-        for 0..BOARD_COLS: (col) {
+    for 0..(BOARD_ROWS - 2) (row) {
+        for 0..BOARD_COLS (col) {
             g := b.at(col, row);
             if g == b.at(col, row + 1) and g == b.at(col, row + 2) { runs += 1; }
         }