refactor: no builds in Dockerfiles, CI builds all artifacts

Dockerfiles now only COPY pre-built artifacts:
- Dockerfile (SaaS): just COPY target/*.jar, no multi-stage build
- ui/sign-in/Dockerfile (Logto): just FROM logto + COPY dist/
- Removed docker/logto.Dockerfile (had node build stage)

CI pipeline builds everything:
- docker job: builds frontend, JAR, sign-in UI, then packages
  into images using the simple Dockerfiles
- Uses cameleer-build:1 (has node + maven + docker)
- build job: also builds sign-in UI for testing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -1,30 +1,7 @@
-# syntax=docker/dockerfile:1
-
-# Frontend: runs natively on build host
-FROM --platform=$BUILDPLATFORM node:22-alpine AS frontend
-ARG REGISTRY_TOKEN
-WORKDIR /ui
-COPY ui/package.json ui/package-lock.json ui/.npmrc ./
-RUN echo "//gitea.siegeln.net/api/packages/cameleer/npm/:_authToken=${REGISTRY_TOKEN}" >> .npmrc && npm ci
-COPY ui/ .
-RUN npm run build
-
-# Maven build: runs natively on build host (no QEMU emulation)
-FROM --platform=$BUILDPLATFORM eclipse-temurin:21-jdk-alpine AS build
-WORKDIR /build
-COPY .mvn/ .mvn/
-COPY mvnw pom.xml ./
-# Cache deps — only re-downloaded when POM changes
-RUN ./mvnw dependency:go-offline -B || true
-COPY src/ src/
-COPY --from=frontend /ui/dist/ src/main/resources/static/
-RUN ./mvnw package -DskipTests -B
-
-# Runtime: target platform (amd64)
 FROM eclipse-temurin:21-jre-alpine
 WORKDIR /app
 RUN addgroup -S cameleer && adduser -S cameleer -G cameleer
-COPY --from=build /build/target/*.jar app.jar
+COPY target/*.jar app.jar
 USER cameleer
 EXPOSE 8080
 ENTRYPOINT ["java", "-jar", "app.jar"]