feat(postal): add postal service addon and bundle pending addon work

- New postal-service-addon: per-player mailboxes + post-office send block
  (ActionForm recipient picker, offline notification queue, chunk-load
  retry via tickingarea)
- Commit previously untracked private-chest, home-sign, keep-inventory
  addons and their docker-compose mounts
- Deploy workflow: add postal + previously unwired addons to path filter
  and checkout list; drop easter-egg from deployment
- enabled_packs.json: register postal UUIDs for Lyla + Mya

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

addon/anthrax_cat_BP/entities/anthrax_cat.json

@@ -3,7 +3,7 @@
   "minecraft:entity": {
     "description": {
       "identifier": "silverlabs:anthrax_cat",
-      "is_spawnable": false,
+      "is_spawnable": true,
       "is_summonable": true,
       "is_experimental": false
     },
@@ -39,18 +39,6 @@
       "minecraft:knockback_resistance": {
         "value": 1.0
       },
-      "minecraft:damage_sensor": {
-        "triggers": [
-          {
-            "cause": "all",
-            "deals_damage": false
-          },
-          {
-            "cause": "override",
-            "deals_damage": true
-          }
-        ]
-      },
       "minecraft:health": {
         "value": 20,
         "max": 20