Fix obvious typos (#2585)

## Summary
- fix obvious spelling typos flagged by codespell across docs, tests,
comments
- no functional changes

## Testing
- pre-commit hooks (eslint/prettier) ran during commit

src/client/graphics/layers/FxLayer.ts

@@ -129,7 +129,7 @@ export class FxLayer implements Layer {
     if (gold > 0) {
       const shortened = renderNumber(gold, 0);
       this.addTextFx(`+ ${shortened}`, x, y);
-      y += 10; // increase y so the next popup starts bellow
+      y += 10; // increase y so the next popup starts below
     }
 
     if (troops > 0) {

src/client/graphics/layers/UnitLayer.ts

@@ -376,7 +376,7 @@ export class UnitLayer implements Layer {
     );
   }
 
-  // interception missle from SAM
+  // interception missile from SAM
   private handleMissileEvent(unit: UnitView) {
     this.drawSprite(unit);
   }