Fourth master: dwarves get their own side so the yellow AI works; yellow colours and texts; AI cores use the player's throne and heart in their colour

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

lang/en.lang

@@ -777,6 +777,8 @@ msg.rival1_attack = Mossgrim, the green master, sends {0} creatures against you!
 msg.rival2_attack = Lady Nightwell, the blue master, sends {0} creatures against you!
 msg.rival1_out = Mossgrim is defeated - his soul core has shattered!
 msg.rival2_out = Lady Nightwell is defeated - her soul core has shattered!
+msg.rival3_attack = Saffrax, the yellow master, sends {0} creatures against you!
+msg.rival3_out = Saffrax is defeated - his soul core has shattered!
 msg.rival_unit_slain = A {0} of a rival master falls! +{1} gold.
 msg.wave_on_rival1 = Wave {0}: {1} heroes march on the green master.
 msg.wave_on_rival2 = Wave {0}: {1} heroes march on the blue master.