fix(camping): use air/liquid check for tent ground + legacy geo format

Two live-testing regressions:

- block.isSolid is not a reliable member of the @minecraft/server Block
  API in BDS 1.26 — it returned undefined, so !b.isSolid was always
  true and every ground cell failed. Replaced with !b.isAir &&
  !b.isLiquid (same predicate the clear-space check below already
  uses), which correctly accepts grass/dirt/stone and only rejects air
  or water/lava.

- The half-slab hammock geometry was silently rejected and rendered
  invisible. The block-model parser wants the legacy 1.12.0 format
  with simple "uv": [0, 0], not 1.21.0 with per-face UV objects.
  Rewritten hammock_slab.geo.json to match the working
  addon/spark_pet_RP/models/blocks/dragon_basket.geo.json format.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

camping-supplies-addon/camping_supplies_RP/models/blocks/hammock_slab.geo.json

@@ -1,32 +1,18 @@
 {
-  "format_version": "1.21.0",
+  "format_version": "1.12.0",
   "minecraft:geometry": [
     {
       "description": {
         "identifier": "geometry.silverlabs.hammock_slab",
         "texture_width": 16,
-        "texture_height": 16,
-        "visible_bounds_width": 2,
-        "visible_bounds_height": 1,
-        "visible_bounds_offset": [0, 0.25, 0]
+        "texture_height": 16
       },
       "bones": [
         {
-          "name": "root",
+          "name": "slab",
           "pivot": [0, 0, 0],
           "cubes": [
-            {
-              "origin": [-8, 0, -8],
-              "size": [16, 4, 16],
-              "uv": {
-                "north": { "uv": [0, 12], "uv_size": [16, 4] },
-                "south": { "uv": [0, 12], "uv_size": [16, 4] },
-                "east":  { "uv": [0, 12], "uv_size": [16, 4] },
-                "west":  { "uv": [0, 12], "uv_size": [16, 4] },
-                "up":    { "uv": [0, 0],  "uv_size": [16, 16] },
-                "down":  { "uv": [0, 0],  "uv_size": [16, 16] }
-              }
-            }
+            { "origin": [-8, 0, -8], "size": [16, 4, 16], "uv": [0, 0] }
           ]
         }
       ]