Drop the pearls currency

Pearls were earned every run and spent on nothing: the aquarium fills up by
finishing worlds, not by paying for it. A counter that only ever goes up is one
more stat competing for attention on the result sheet and the home screen, and
one more field to carry through the run payload, the progress file and both test
suites.

Stars and the animal ladder already say how a run went, so nothing is lost.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/src/lib/tippen/grading.ts

@@ -35,8 +35,6 @@ export interface RunResult {
   animal: AnimalId;
   /** Whether this run unlocks the next lesson on its own. */
   passed: boolean;
-  /** Pearls earned - the aquarium currency. */
-  pearls: number;
   /** Kept for the race-mode ghost and the per-key stats. */
   strokes: readonly Stroke[];
 }
@@ -162,12 +160,6 @@ export function isPassed(accuracy: number): boolean {
   return accuracy >= STAR_THRESHOLDS.two;
 }
 
-/** One pearl per five correct keys, plus a bonus per star. Small numbers that go up
- * every single run, including a bad one - the aquarium should never stall. */
-function pearlsFor(characters: number, stars: number): number {
-  return Math.floor(characters / 5) + stars * 2;
-}
-
 export function grade(state: RunState): RunResult {
   const characters = state.strokes.filter((stroke) => stroke.correct).length;
   const errors = state.missed.size;
@@ -196,7 +188,6 @@ export function grade(state: RunState): RunResult {
     stars,
     animal: animalFor(points).id,
     passed: isPassed(accuracy),
-    pearls: pearlsFor(characters, stars),
     strokes: state.strokes,
   };
 }