Docker build cache: .dockerignore, cache mount, layer reorder, restart script

- .dockerignore: exclude node_modules/.git/tmp/data/logs
- Dockerfile: BuildKit cache mount for npm, --omit=dev at install, drop
  npm prune step
- Reorder layers: shared/src/frontend copy before build, server copy +
  better-sqlite3 rebuild after. Server/shared changes no longer invalidate
  frontend build layer unless shared (FE dep) changes
- Remove duplicate shared COPY in runtime stage (bundled in FE build)
- docker/restart.sh: stop + rebuild + start in one script

docker/Dockerfile

@@ -1,4 +1,5 @@
-# docker/Dockerfile — single container: caddy (front) + node (back).
+# syntax=docker/dockerfile:1
+# docker/Dockerfile --- single container: caddy (front) + node (back).
 # Build context = repo root.
 # ---- build stage: frontend + install backend deps ----
 FROM node:18-alpine AS build
@@ -7,25 +8,26 @@ WORKDIR /app
 COPY package*.json ./
 COPY shared/package.json ./shared/
 COPY server/package.json ./server/
-RUN npm install --include-workspace-root
+RUN --mount=type=cache,target=/root/.npm \
+    npm install --include-workspace-root --omit=dev --prefer-offline
 
+# frontend code (changes often)
 COPY shared/ ./shared/
-COPY server/ ./server/
 COPY src/ ./src/
 COPY public/ ./public/
 COPY tailwind.config.js postcss.config.js ./
 
-# better-sqlite3 native build (alpine musl)
-RUN cd server && npm rebuild better-sqlite3
-
 # build frontend (server storage, same-origin /api + /ws via caddy)
 ARG REACT_APP_TRACKER_APP_ID=ttrpg-initiative-tracker-default
 ENV REACT_APP_STORAGE=server
 ENV REACT_APP_TRACKER_APP_ID=$REACT_APP_TRACKER_APP_ID
 RUN NODE_OPTIONS=--openssl-legacy-provider npm run build
 
-# prune backend dev deps for runtime
-RUN npm prune --omit=dev
+# server after backend - it's fast. so changing server only doesnt invalidate slow frontend.
+COPY server/ ./server/
+# better-sqlite3 native build (alpine musl). Cached if server unchanged.
+RUN cd server && npm rebuild better-sqlite3
+
 
 # ---- runtime stage: caddy + node ----
 FROM node:18-alpine
@@ -38,7 +40,6 @@ COPY --from=build /app/server/node_modules ./server/node_modules
 COPY --from=build /app/package*.json ./
 COPY --from=build /app/shared/package.json ./shared/
 COPY --from=build /app/server/package.json ./server/
-COPY shared/ ./shared/
 COPY server/ ./server/
 # built frontend served by caddy
 COPY --from=build /app/build /srv