Breed at the Day-Care, hatch Eggs, draw MAIL stationery and browse the Hall of Fame (Closes #29)

- Day-Care and breeding: deposits, withdrawal pricing and growth,
  compatibility, egg species, DVs and moves, DayCareStep, egg
  collection and the Odd Egg, compared with the cartridge's routines.
- CountStep: walking happiness, DoEggStep, DayCareStep and DoBikeStep
  in the original's order; HatchEggs with the ROM's hatch animation,
  compared frame by frame with the original.
- MAIL: all ten stationery types and the Portrait MAIL picture,
  compared with the cartridge's tilemaps, graphics and palettes.
- Printing: Bill's PC boxes, Pokedex PRNT, MAIL and the Photo Studio
  take the original's absent-printer path.
- Hall of Fame records (saved apart from the League flag, ready for the
  League to call) and the Hall of Fame PC, compared with the cartridge's
  _HallOfFamePC on 255 pages.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/game/party/eggs.ts

@@ -0,0 +1,42 @@
+import type { PartyMon } from "./pokemon";
+
+/** The happiness a Pokémon has just after hatching (HatchEggs: `ld [hl], $78`),
+ * which replaces the Egg's remaining cycles. */
+export const HATCHED_HAPPINESS = 0x78;
+
+/** The counters CountStep keeps in work RAM (wStepCount,
+ * wPoisonStepCount) and StepHappiness's toggle (wHappinessStepCount). */
+export interface StepCounters {
+  stepCount: number;
+  poisonStepCount: number;
+  happinessStepCount: number;
+}
+
+/** StepHappiness (engine/events/happiness_egg.asm): called each time
+ * wStepCount wraps (every 256 steps), it raises the happiness of every
+ * Pokémon that is not an Egg by one on every other call, so once per 512
+ * steps, up to 255. It does not go through ChangeHappiness: no bonus and
+ * no cap other than the byte's, and a Pokémon already at 255 stays there. */
+export function stepHappiness(
+  counters: Pick<StepCounters, "happinessStepCount">,
+  party: PartyMon[],
+) {
+  counters.happinessStepCount = (counters.happinessStepCount + 1) & 1;
+  if (counters.happinessStepCount) return;
+  for (const mon of party)
+    if (!mon.egg) mon.happiness = Math.min(0xff, mon.happiness + 1);
+}
+
+/** DoEggStep (engine/pokemon/breeding.asm): from the first slot, each Egg's
+ * cycles (kept in its happiness byte) drop by one until one reaches zero,
+ * which ends the loop and reports that an Egg is ready to hatch; the Eggs
+ * after it are not counted down on that step. A byte already at zero
+ * wraps to 255 (`dec [hl]` has no floor) and does not hatch. */
+export function doEggStep(party: PartyMon[]): boolean {
+  for (const mon of party) {
+    if (!mon.egg) continue;
+    mon.happiness = (mon.happiness - 1) & 0xff;
+    if (!mon.happiness) return true;
+  }
+  return false;
+}