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).

backend/Dockerfile

@@ -0,0 +1,7 @@
+FROM oven/bun:latest
+WORKDIR /app
+COPY package.json tsconfig.json ./
+RUN bun install
+COPY src ./src
+EXPOSE 3000
+CMD ["bun", "run", "src/index.ts"]