feat(player): join in progress + DISABLED en agotar vidas (Fase 1)

Habilita la regla 1 de la nova FSM de joc: durant PLAYING, qualsevol
slot DISABLED pot pulsar START per entrar a partida amb spawn aeri al
seu costat de la porta i vides reseteades. Quan un jugador esgota les
vides, `respawnFromDying` el deixa a DISABLED i publica `player_disabled`
al bus; GameScene i HUD reaccionen, deixant el slot disponible per a un
nou join. Afegeix prompts al HUD ("PULSA START / PER JUGAR" o
"ESPERA / PER JUGAR") segons l'estat de la RoomFsm.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

data/locale/en.yaml

@@ -38,6 +38,13 @@ hud:
   treasures: "Tre"
   pyramid: "Pyramid"
   room: "Room"
+  # Prompts shown in an inactive slot's block (instead of zeros) while
+  # a player hasn't pressed START yet or has run out of lives. Two
+  # short lines so they fit in the side block (~106 px wide).
+  join_prompt_can_join_l1: "PRESS START"
+  join_prompt_can_join_l2: "TO PLAY"
+  join_prompt_wait_l1: "PLEASE"
+  join_prompt_wait_l2: "WAIT"
 
 # Texts of the TITLE scene.
 title: