fix(docker): add python3/make/g++ for native module rebuilds; clarify DEV docs

- @discordjs/opus@0.10.0 has no node>=22 prebuilt, so node-gyp falls back
  to source compile and needs python3/make/g++. Add them to apt-get install
  in the bookworm-slim base. Verified `docker build` succeeds end-to-end.
- .env.example: rewrite DEV description to cover both behaviors
  (clientReady guild-only registration + Prod-commands guild-wipe-then-global).

Dockerfile

@@ -1,7 +1,7 @@
 FROM node:22-bookworm-slim
 
 RUN apt-get update \
-    && apt-get install -y --no-install-recommends ffmpeg \
+    && apt-get install -y --no-install-recommends ffmpeg python3 make g++ \
     && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app