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/match_detect.sx

@@ -11,7 +11,7 @@ t :: #import "test.sx";
 // Inverse of `gem_char`: map a gem character back to its Gem so each board can
 // be written as a human-readable grid of GEM_CHARS.
 char_to_gem :: (c: u8) -> Gem {
-    for 0..GEM_COUNT: (i) {
+    for 0..GEM_COUNT (i) {
         if GEM_CHARS[i] == c { return cast(Gem) i; }
     }
     .red
@@ -22,9 +22,9 @@ char_to_gem :: (c: u8) -> Gem {
 // assert the matched-cell count.
 scene :: (name: string, rows: []string, want_count: s64) {
     b : Board = ---;
-    for 0..BOARD_ROWS: (row) {
+    for 0..BOARD_ROWS (row) {
         line := rows[row];
-        for 0..BOARD_COLS: (col) {
+        for 0..BOARD_COLS (col) {
             b.set(col, row, char_to_gem(line[col]));
         }
     }