chore: Radicle CI build contract

.radicle/native.yaml

@@ -0,0 +1,2 @@
+shell: |
+  ci-build

Dockerfile

@@ -1,5 +1,12 @@
-# Build stage: compile the Vite/TS app
-FROM node:22-alpine AS build
+# Radicle CI build contract (ci-build): image name = ${CAT}/${APP}
+ARG CAT=tessera
+ARG APP=skytess
+
+# Build stage: compile the Vite/TS app. Pinned to the BUILD host platform: the
+# stage output (dist/) is arch-independent static files, so the heavy pnpm/vite
+# part runs natively on the CI host while the final stage (COPY-only) can target
+# any arch without emulation.
+FROM --platform=$BUILDPLATFORM node:22-alpine AS build
 # Pinned, NOT pnpm@11: a floating major picks up whatever 11.x is newest at
 # build time and has broken this build before (11.11 tightened the allowBuilds
 # matcher). Keep this in lockstep with package.json's packageManager field.