CI: add rust/ build+test workflow

data/dungeons/mangar_4.json

@@ -0,0 +1,32 @@
+{
+  "id": "mangar_4",
+  "name": "Mangar's Tower - Level 4",
+  "dungeon": "mangar",
+  "level": 4,
+  "width": 22,
+  "height": 22,
+  "description": "The fourth level of Mangar's Tower. Mangar's most powerful lieutenants stand guard. The final approach to Mangar's sanctum.",
+  "encounter_level": 8,
+  "special_squares": [
+    { "x": 0, "y": 0, "type": "stairs_up", "destination": "mangar_3", "label": "Return to Mangar's Tower Level 3" },
+    { "x": 21, "y": 21, "type": "stairs_down", "destination": "mangar_5", "label": "Descend to Mangar's Throne Room" },
+    { "x": 10, "y": 4, "type": "special_encounter", "text": "An Archmage serves Mangar! A powerful spellcaster!", "encounter": "archmage" },
+    { "x": 5, "y": 6, "type": "special_encounter", "text": "A Lich! Undead master of necromancy serves Mangar!", "encounter": "lich" },
+    { "x": 16, "y": 3, "type": "anti_magic", "text": "Mangar's personal wards. Even the strongest spells are negated." },
+    { "x": 8, "y": 9, "type": "trap", "text": "Mangar's ultimate trap! Every element attacks at once!", "damage": "5d8" },
+    { "x": 14, "y": 8, "type": "darkness", "text": "Absolute magical darkness. Not even true seeing penetrates it." },
+    { "x": 3, "y": 12, "type": "spinner", "text": "The tower itself seems to rotate. You have no idea which way is forward." },
+    { "x": 18, "y": 11, "type": "silence", "text": "Mangar's god-tier silence spell. Reality itself goes quiet." },
+    { "x": 11, "y": 14, "type": "special_encounter", "text": "A Storm Giant loyal to Mangar hurls lightning bolts!", "encounter": "storm_giant" },
+    { "x": 6, "y": 17, "type": "trap", "text": "Mangar's personal curse afflicts you! Strength drains away.", "damage": "2d10" },
+    { "x": 19, "y": 16, "type": "special_encounter", "text": "A Death Denizen! An avatar of death itself!", "encounter": "death_denizen" },
+    { "x": 15, "y": 19, "type": "message", "text": "You feel Mangar's presence growing stronger with every step." },
+    { "x": 2, "y": 8, "type": "special_encounter", "text": "Mangar's elite guard - a formation of powerful undead knights!", "encounter": "death_knights" },
+    { "x": 20, "y": 5, "type": "trap", "text": "Temporal trap! You age 10 years in an instant!", "damage": "3d6" },
+    { "x": 13, "y": 18, "type": "message", "text": "The door to Mangar's throne room gleams with dark enchantments." }
+  ],
+  "connections": [
+    { "from_x": 21, "from_y": 21, "to": "mangar_5", "type": "stairs_down" },
+    { "from_x": 0, "from_y": 0, "to": "mangar_3", "type": "stairs_up" }
+  ]
+}