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

.dockerignore

@@ -0,0 +1,11 @@
+node_modules
+**/node_modules
+.git
+tmp
+data
+*.log
+npm-debug.log*
+.DS_Store
+.env*
+coverage
+.nyc_output