feat(UC-02): data-driven room themes — 6 JSON + consumer migration + cleanup

Phase 3: Extract 6 themes into JSON (oubliette, inferno, crypt, ice, sculk, sandstone)
Phase 4: Migrate HangingCagePiece to use RoomThemeRegistry.pickRandomOrFallback()
  - Move 7 shared static methods from RoomTheme into HangingCagePiece
  - Replace per-enum placeDecorations() with generic DecorationConfig-based placement
Phase 5: Delete RoomTheme.java (-1368L)

src/main/resources/data/tiedup/tiedup_room_themes/sculk.json

@@ -0,0 +1,58 @@
+{
+  "weight": 10,
+  "wall_palette": {
+    "default": [
+      { "block": "minecraft:cracked_deepslate_bricks", "weight": 0.10 },
+      { "block": "minecraft:sculk", "weight": 0.30 },
+      { "block": "minecraft:deepslate_bricks", "weight": 0.60 }
+    ]
+  },
+  "floor_palette": {
+    "default": [
+      { "block": "minecraft:sculk", "weight": 0.30 },
+      { "block": "minecraft:deepslate_tiles", "weight": 0.70 }
+    ],
+    "edge": [
+      { "block": "minecraft:sculk", "weight": 1.0 }
+    ]
+  },
+  "ceiling_palette": {
+    "default": [
+      { "block": "minecraft:cracked_deepslate_bricks", "weight": 0.10 },
+      { "block": "minecraft:sculk", "weight": 0.20 },
+      { "block": "minecraft:deepslate_bricks", "weight": 0.70 }
+    ]
+  },
+  "wall_shell": "minecraft:deepslate_bricks",
+  "wall_accent": "minecraft:sculk_catalyst",
+  "pillar_palette": {
+    "default": [
+      { "block": "minecraft:sculk", "weight": 0.30 },
+      { "block": "minecraft:deepslate_tile_wall", "weight": 0.70 }
+    ],
+    "cap": [
+      { "block": "minecraft:sculk", "weight": 1.0 }
+    ]
+  },
+  "scatter_palette": {
+    "default": [
+      { "block": "minecraft:sculk", "weight": 0.50 },
+      { "block": "minecraft:sculk_vein", "weight": 0.30 },
+      { "block": "minecraft:moss_carpet", "weight": 0.20 }
+    ]
+  },
+  "decorations": {
+    "wall_midpoint_blocks": [
+      { "block": "minecraft:sculk_vein", "y_offset": 2 },
+      { "block": "minecraft:soul_lantern", "y_offset": 3 }
+    ],
+    "first_corner_special": { "block": "minecraft:sculk_catalyst", "y_offset": 1 },
+    "furniture_cluster": [
+      { "block": "minecraft:sculk_shrieker", "y_offset": 1 },
+      { "block": "minecraft:sculk_sensor", "y_offset": 1 },
+      { "block": "minecraft:candle[lit=true,candles=3]", "y_offset": 1 }
+    ],
+    "use_torch_lighting": false,
+    "has_ceiling_chain": true
+  }
+}