fix(mobile): align LVLS button with d-pad's bottom arrow row

Restructure .dock-left from a 3-button column-flex into a 2x2 grid:
UNDO and RESET share the top row, LVLS spans the full bottom row via
grid-column: 1 / -1. Both columns now share 48px row heights and a 6px
gap so UNDO/RESET line up with UP and LVLS lines up with the
LEFT/DOWN/RIGHT row.

Bump .action height 44 -> 48px on coarse pointers so action rows match
the d-pad's 48px arrows. Still well above the 44pt HIG minimum. With
the action stack now equal to the d-pad's natural height (102px), the
dock no longer needs the previous round's asymmetric flex-end layout
to look balanced.

src/views/MobileControls.svelte

@@ -125,11 +125,21 @@
             box-sizing: border-box;
         }
 
+        /* Action buttons mirror the d-pad as a 2-row grid:
+             row 1: UNDO + RESET (matches UP row)
+             row 2: LVLS spans both columns (matches LEFT/DOWN/RIGHT row)
+           Both columns share the same row heights / gap so action and arrow
+           rows line up on the same Y. */
         .dock-left {
-            display: flex;
-            flex-direction: column;
-            justify-content: flex-end;
-            gap: 8px;
+            display: grid;
+            grid-template-columns: auto auto;
+            grid-auto-rows: 48px;
+            gap: 6px;
+            align-self: flex-start;
+        }
+
+        .dock-left .action:nth-child(3) {
+            grid-column: 1 / -1;
         }
 
         .dpad {
@@ -142,6 +152,10 @@
             gap: 6px;
             align-self: flex-start;
         }
+
+        /* Match arrow height for grid-row alignment between action stack
+           and d-pad. Still well above the 44pt HIG minimum. */
+        .action { height: 48px; }
     }
 
     /* Global `button` rules (touch-action, tap-highlight) live in app.css. */