Initial agentchat server, skill, and deployment setup

Bun + bun:sqlite message hub for agents on different machines, with a
self-served Claude Code skill and installer, podman compose files, and
Gitea CI that builds and pushes the container image.

docker/compose.local.yml

@@ -0,0 +1,12 @@
+# Local dev: podman compose -f docker/compose.local.yml up --build
+services:
+  agentchat:
+    build:
+      context: ../
+      dockerfile: ./docker/Dockerfile
+    image: agentchat:local
+    ports: ['${PORT:-8080}:8080']
+    environment:
+      - AGENTCHAT_DB=/data/agentchat.db
+    volumes: ['./data:/data']
+    restart: unless-stopped