Swap textAlign so labels extend into tile, not off-edge

User feedback: text on the left edge ('left' align) was getting
cut off because the text extended to negative X (off the left
edge of the canvas). Same problem on the right.

Fix: swap the textAlign so each side's text extends INTO the tile,
not OFF the edge:
- Left-side labels (S, N) now use textAlign 'right'. Anchor at
  the left edge of the tile area; the text's right edge is at
  the anchor and it extends rightward into the tile.
- Right-side labels (y, x) use textAlign 'left'. Anchor at the
  right edge; the text's left edge is at the anchor and extends
  leftward into the tile.

Mirror (scale -1, 1) is still applied so the text content is
flipped.

vendor/clouds3d.js

@@ -379,16 +379,19 @@ function drawTileAt(lng, perp, dx, dz, centerTileX, centerTileY) {
             groundCtx.fillText(text, 0, 0);
             groundCtx.restore();
         }
-        // S at top-left (image south after Y mirror is at canvas top)
-        mirrorLabel('S', canvasX + 12, canvasY + 44, 'left');
-        // N at bottom-left (image north at canvas bottom)
-        mirrorLabel('N', canvasX + 12, canvasY + 244, 'left');
+        // S at top-left, textAlign 'right' so the text's right edge
+        // is at the anchor (text extends into the tile from the left
+        // edge of the tile area).
+        mirrorLabel('S', canvasX + 12, canvasY + 44, 'right');
+        // N at bottom-left
+        mirrorLabel('N', canvasX + 12, canvasY + 244, 'right');
         // Tile coordinates, top-right and bottom-right corners
         groundCtx.font = 'bold 18px monospace';
-        // y at top-right
-        mirrorLabel('y=' + tileY, canvasX + GROUND_TILE_SIZE - 12, canvasY + 28, 'right');
+        // y at top-right, textAlign 'left' so text extends into the
+        // tile from the right edge.
+        mirrorLabel('y=' + tileY, canvasX + GROUND_TILE_SIZE - 12, canvasY + 28, 'left');
         // x at bottom-right
-        mirrorLabel('x=' + tileX, canvasX + GROUND_TILE_SIZE - 12, canvasY + GROUND_TILE_SIZE - 12, 'right');
+        mirrorLabel('x=' + tileX, canvasX + GROUND_TILE_SIZE - 12, canvasY + GROUND_TILE_SIZE - 12, 'left');
 
         return true;
     }).catch(function() {