Add self-hosted RCS backend, extension, and ops tooling

Ship the Go/SQLite API and Web UI, Chrome/Brave capture addon,
Docker Compose, Pangolin reverse-proxy support, and a user-crontab
watchdog so the binary stays running without systemd.

docker-compose.yml

@@ -0,0 +1,17 @@
+services:
+  rcs:
+    build:
+      context: ./backend
+      dockerfile: Dockerfile
+    ports:
+      - "8080:8080"
+    environment:
+      RCS_ADDR: "0.0.0.0:8080"
+      RCS_DATA_DIR: /data
+      RCS_API_KEY: "${RCS_API_KEY:-}"
+      RCS_PUBLIC_BASE_URL: "${RCS_PUBLIC_BASE_URL:-}"
+      RCS_TRUST_PROXY: "${RCS_TRUST_PROXY:-}"
+      IMGUR_CLIENT_ID: "${IMGUR_CLIENT_ID:-}"
+    volumes:
+      - ./data:/data
+    restart: unless-stopped