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.

board_fx.sx

@@ -123,7 +123,7 @@ BoardFxAssets :: struct {
     loaded: bool;
 
     init :: (self: *BoardFxAssets) {
-        for 0..GEM_COUNT: (t) { self.tex[t] = 0; }
+        for 0..GEM_COUNT (t) { self.tex[t] = 0; }
         self.loaded = false;
     }
 
@@ -144,7 +144,7 @@ BoardFxAssets :: struct {
         // (sx codegen), so the per-pixel tint loop only ASSIGNS pre-declared vars.
         i : s64 = 0;
         o : s64 = 0;
-        for 0..GEM_COUNT: (t) {
+        for 0..GEM_COUNT (t) {
             col := fx_tint(t);
             i = 0;
             while i < n {
@@ -219,7 +219,7 @@ BoardFx :: struct {
         // Whole-move depth boost: a deeper cascade makes every burst bigger from
         // its first round, escalating in lockstep with the cascade SFX cue.
         depth_boost := FX_BURST_DEPTH * cast(f32) fx_combo_level(mv.rounds.len);
-        for 0..mv.rounds.len: (k) {
+        for 0..mv.rounds.len (k) {
             rd := @mv.rounds.items[k];
             t0 := SWAP_ANIM_DUR + cast(f32) k * (CLEAR_ANIM_DUR + FALL_ANIM_DUR);
             extra := depth_boost + FX_BURST_COMBO * cast(f32) min(k, 2);
@@ -227,7 +227,7 @@ BoardFx :: struct {
             // bursts ripple in lockstep with the staggered pops (P18.2) instead of
             // one simultaneous flash. The round's audio cue still fires once at t0.
             span := clear_diag_span(@rd.matched);
-            for 0..BOARD_CELLS: (idx) {
+            for 0..BOARD_CELLS (idx) {
                 if rd.matched.cells[idx] {
                     g := rd.before[idx];
                     if g != .empty {
@@ -253,7 +253,7 @@ BoardFx :: struct {
         sc : s64 = 0;
         sr : s64 = 0;
         cnt : s64 = 0;
-        for 0..BOARD_CELLS: (idx) {
+        for 0..BOARD_CELLS (idx) {
             if rd0.matched.cells[idx] {
                 sc += idx % BOARD_COLS;
                 sr += idx / BOARD_COLS;