chore: initial commit of foundryvtt-admin

Spun out of the hbm-books working folder into its own repo. A small
backend+frontend+COBOL admin tool for managing Foundry VTT worlds
(socket inspection, join/shutdown debugging).

frontend/Dockerfile

@@ -0,0 +1,7 @@
+FROM node:20-alpine
+WORKDIR /app
+COPY package.json tsconfig.json vite.config.ts index.html ./
+RUN npm install
+COPY src ./src
+EXPOSE 5173
+CMD ["npm", "run", "dev"]