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>

postal-service-addon/postal_service_RP/blocks.json

@@ -0,0 +1,5 @@
+{
+  "format_version": [1, 1, 0],
+  "silverlabs:mailbox": { "sound": "stone" },
+  "silverlabs:post_office": { "sound": "wood" }
+}

postal-service-addon/postal_service_RP/manifest.json

@@ -0,0 +1,17 @@
+{
+  "format_version": 2,
+  "header": {
+    "name": "Postal Service Resources",
+    "description": "Textures and lang for silverlabs:mailbox and silverlabs:post_office",
+    "uuid": "d7a4b9c1-2e3f-4a5b-8c6d-1f2e3d4c5b63",
+    "version": [1, 0, 0],
+    "min_engine_version": [1, 21, 0]
+  },
+  "modules": [
+    {
+      "type": "resources",
+      "uuid": "d7a4b9c1-2e3f-4a5b-8c6d-1f2e3d4c5b64",
+      "version": [1, 0, 0]
+    }
+  ]
+}

postal-service-addon/postal_service_RP/texts/en_US.lang

@@ -0,0 +1,2 @@
+tile.silverlabs:mailbox.name=Mailbox
+tile.silverlabs:post_office.name=Post Office

postal-service-addon/postal_service_RP/textures/terrain_texture.json

@@ -0,0 +1,14 @@
+{
+  "resource_pack_name": "postal_service_RP",
+  "texture_name": "atlas.terrain",
+  "padding": 8,
+  "num_mip_levels": 4,
+  "texture_data": {
+    "mailbox": {
+      "textures": "textures/blocks/mailbox"
+    },
+    "post_office": {
+      "textures": "textures/blocks/post_office"
+    }
+  }
+}