feat(pewpewstudio): laser job studio on nh3-docker :8185 (api + Caddy front), Homepage tile

Prime's directive via pewpew-dev. Images are built on nh3-dev from a clean
archive of vh/pewpewstudio (26bba3c; hamr over gitea SSH via BuildKit --ssh)
and loaded on nh3-docker. Caddy serves the SPA and strips /api/ in front of
the backend. It refuses foreign Host headers inside a route block, because the
Host rewrite would otherwise bypass the backend's TrustedHost. The DB, assets
and the app-edited shop config live on named volumes inside nh3-docker's
nightly vzdump. Verified: SPA, /api/machines and /api/generate/workflows 200;
foreign Host 400.

stacks/pewpewstudio/.env.example

@@ -0,0 +1,4 @@
+PEWPEW_REV=26bba3c
+PORT=8185
+# Set both Worldtree vars or neither (WORLDTREE_BASE_URL is in compose.yaml):
+WORLDTREE_API_KEY=   # secret get nh3-dev/.config/worldtree/pewpewstudio-demo-key