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>

docker/logto.Dockerfile

@@ -1,14 +0,0 @@
-# syntax=docker/dockerfile:1
-
-# Build custom sign-in UI
-FROM --platform=$BUILDPLATFORM node:22-alpine AS sign-in
-ARG REGISTRY_TOKEN
-WORKDIR /ui
-COPY ui/sign-in/package.json ui/sign-in/package-lock.json ui/sign-in/.npmrc ./
-RUN echo "//gitea.siegeln.net/api/packages/cameleer/npm/:_authToken=${REGISTRY_TOKEN}" >> .npmrc && npm ci
-COPY ui/sign-in/ .
-RUN npm run build
-
-# Custom Logto with baked-in sign-in UI
-FROM ghcr.io/logto-io/logto:latest
-COPY --from=sign-in /ui/dist/ /etc/logto/packages/experience/dist/