build: add Earthfile with a dist target (mirrors lunar plugin build)

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: idelvall

Earthfile

@@ -0,0 +1,18 @@
+VERSION 0.8
+FROM node:25-alpine3.21
+
+deps:
+  WORKDIR /json
+  COPY package.json package-lock.json tsconfig.json ./
+  RUN --mount=type=cache,target=/root/.npm npm ci
+  COPY --dir .config .
+
+src:
+  FROM +deps
+  COPY LICENSE CHANGELOG.md ./
+  COPY --dir src .
+
+dist:
+  FROM +src
+  RUN npm run build
+  SAVE ARTIFACT dist AS LOCAL dist