CI: add rust/ build+test workflow

data/dungeons/mangar_3.json

@@ -0,0 +1,31 @@
+{
+  "id": "mangar_3",
+  "name": "Mangar's Tower - Level 3",
+  "dungeon": "mangar",
+  "level": 3,
+  "width": 22,
+  "height": 22,
+  "description": "The third level of Mangar's Tower. The most dangerous summoned creatures roam these halls. Only the strongest parties survive.",
+  "encounter_level": 7,
+  "special_squares": [
+    { "x": 0, "y": 0, "type": "stairs_up", "destination": "mangar_2", "label": "Return to Mangar's Tower Level 2" },
+    { "x": 21, "y": 21, "type": "stairs_down", "destination": "mangar_4", "label": "Descend to Mangar's Tower Level 4" },
+    { "x": 11, "y": 5, "type": "special_encounter", "text": "A Black Dragon! Its breath weapon could annihilate the party!", "encounter": "black_dragon" },
+    { "x": 5, "y": 3, "type": "special_encounter", "text": "A Demon Lord of Mangar's court stands before you!", "encounter": "demon_lord" },
+    { "x": 16, "y": 4, "type": "anti_magic", "text": "Mangar's inner wards. Magic is almost completely suppressed." },
+    { "x": 7, "y": 8, "type": "trap", "text": "Mangar's death trap! Poison, fire, and acid spray simultaneously!", "damage": "4d8" },
+    { "x": 14, "y": 9, "type": "darkness", "text": "Living darkness that actively resists light sources." },
+    { "x": 3, "y": 12, "type": "spinner", "text": "The maze spell here is permanent. Even mapping doesn't help." },
+    { "x": 18, "y": 13, "type": "silence", "text": "Mangar's supreme silence. The absence of sound is suffocating." },
+    { "x": 9, "y": 16, "type": "special_encounter", "text": "The Ancient Enemy! A being from beyond this world!", "encounter": "ancient_enemy" },
+    { "x": 20, "y": 17, "type": "trap", "text": "A dimensional rift opens! Chaotic energy tears at reality!", "damage": "3d10" },
+    { "x": 6, "y": 19, "type": "message", "text": "Mangar's throne room is close. The air crackles with power." },
+    { "x": 15, "y": 18, "type": "special_encounter", "text": "A Balrog! Whip of fire and shadow!", "encounter": "balrog" },
+    { "x": 2, "y": 15, "type": "trap", "text": " summoned elementals burst from the walls!", "damage": "3d6" },
+    { "x": 17, "y": 6, "type": "message", "text": "A treasury room - piles of gold and gems. A distraction or a reward?" }
+  ],
+  "connections": [
+    { "from_x": 21, "from_y": 21, "to": "mangar_4", "type": "stairs_down" },
+    { "from_x": 0, "from_y": 0, "to": "mangar_2", "type": "stairs_up" }
+  ]
+}