feat: A-frame tent + portal walk-through field + texture polish

- camping: replace cube tent with A-frame slope panels (tent_panel_l/r) +
  cardinal_direction permutations; vote-skip sleep that mixes
  player.isSleeping bed sleepers with tent occupants and respects the
  playersSleepingPercentage gamerule; new weathered-canvas texture.
- lobby: walk-through silverlabs:portal_field block (no collision,
  translucent swirl, cross-plane geo) auto-placed above each portal frame;
  invisible silverlabs:portal_label entity floats above each portal with
  the destination world name; transfer detection now scans down through
  the field to find the destination frame.
- postal: regenerate post_office and mailbox block textures so they fill
  the full block face (brick + POST plaque, full red panel with slot/latch
  /flag/rivets) instead of small sprites floating on transparent.
- dynamite + tow-boat: ship the addons (volumes wired into all four
  worlds; enabled_packs registers them into Mya's world).
- art: build-textures.py extended; build-art-catalog.py added to project.

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

tow-boat-addon/tow_boat_RP/textures/item_texture.json

@@ -0,0 +1,9 @@
+{
+  "resource_pack_name": "tow_boat_RP",
+  "texture_name": "atlas.items",
+  "texture_data": {
+    "tow_boat": {
+      "textures": "textures/items/tow_boat"
+    }
+  }
+}