fix(camping): half-slab hammock geometry + smarter tent grounding

- Hammock now uses a custom geometry.silverlabs.hammock_slab (8-voxel
  tall half-slab instead of a full cube), matching its thin collision
  box so the block reads visually as a hammock cradle, not a brick.

- Tent placement now projects the player's feet down to the nearest
  solid block (up to 3 blocks) before picking the base Y, so mid-jump
  fractional positions or standing-on-slab cases don't mis-place the
  footprint one block too high.

- Failure messages now include the exact failing cell coordinates and
  the block type that's in the way, so we can diagnose live pitch
  attempts without guesswork.

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

camping-supplies-addon/camping_supplies_BP/blocks/hammock_cloth.json

@@ -26,7 +26,7 @@
         "origin": [-8, 0, -8],
         "size": [16, 4, 16]
       },
-      "minecraft:geometry": "minecraft:geometry.full_block",
+      "minecraft:geometry": "geometry.silverlabs.hammock_slab",
       "minecraft:light_dampening": 0
     }
   }