CI: add rust/ build+test workflow

data/dungeons/sewers_2.json

@@ -0,0 +1,31 @@
+{
+  "id": "sewers_2",
+  "name": "Sewers - Level 2",
+  "dungeon": "sewers",
+  "level": 2,
+  "width": 22,
+  "height": 22,
+  "description": "The middle sewers. The water is deeper here and the goblins are better organized. Their chieftain lurks somewhere below.",
+  "encounter_level": 2,
+  "special_squares": [
+    { "x": 0, "y": 0, "type": "stairs_up", "destination": "sewers_1", "label": "Return to Sewers Level 1" },
+    { "x": 21, "y": 21, "type": "stairs_down", "destination": "sewers_3", "label": "Descend to Sewers Level 3" },
+    { "x": 10, "y": 2, "type": "trap", "text": "A goblin tripwire! You fall face-first into the muck.", "damage": "1d4" },
+    { "x": 6, "y": 6, "type": "spinner", "text": "The tunnels curve sharply. You lose your bearings." },
+    { "x": 15, "y": 4, "type": "darkness", "text": "No torches here. The darkness is absolute." },
+    { "x": 3, "y": 10, "type": "special_encounter", "text": "A goblin shaman chants in a side chamber!", "encounter": "goblin_shaman" },
+    { "x": 18, "y": 9, "type": "anti_magic", "text": "Glowing crystals embedded in the walls absorb magical energy." },
+    { "x": 8, "y": 14, "type": "trap", "text": "A poison gas trap! Green vapors fill the corridor.", "damage": "2d6" },
+    { "x": 14, "y": 16, "type": "message", "text": "A goblin lookout post. Empty now, but recently abandoned." },
+    { "x": 5, "y": 18, "type": "silence", "text": "The echoing water sounds suddenly cut off. Unnatural silence." },
+    { "x": 20, "y": 14, "type": "message", "text": "Graffiti: 'Wraith Lord Below - Turn Back' written in blood." },
+    { "x": 11, "y": 11, "type": "spinner", "text": "The water current swirls around your legs, disorienting you." },
+    { "x": 17, "y": 19, "type": "special_encounter", "text": "A goblin chieftain's bodyguard challenges you!", "encounter": "goblin_elite" },
+    { "x": 2, "y": 15, "type": "trap", "text": "Crossbow bolt fires from a hidden slot in the wall!", "damage": "1d8" },
+    { "x": 9, "y": 8, "type": "message", "text": "The stench is unbearable here. You retch but press on." }
+  ],
+  "connections": [
+    { "from_x": 21, "from_y": 21, "to": "sewers_3", "type": "stairs_down" },
+    { "from_x": 0, "from_y": 0, "to": "sewers_1", "type": "stairs_up" }
+  ]
+}