Add Django site, Docker packaging, and beta/prod Gitea deploys.

Unignore site/ (was blocked by mkdocs /site rule), add compose/Docker/uv tooling, and split deploys so push to main goes to beta while prod stays manual.

site/messaging/providers/postcard/postgrid.py

@@ -0,0 +1,22 @@
+"""PostGrid postcard adapter."""
+
+from dataclasses import dataclass
+
+from django.conf import settings
+
+from messaging.providers.postcard import PostcardResult
+
+
+@dataclass
+class PostGridProvider:
+    name: str = "postgrid"
+
+    def send_postcard(self, message) -> PostcardResult:
+        if not settings.POSTGRID_API_KEY:
+            raise RuntimeError("POSTGRID_API_KEY is not configured")
+        raise NotImplementedError(
+            "PostGrid adapter stub — configure account then implement send"
+        )
+
+    def get_status(self, provider_id: str) -> str:
+        return "unknown"