feat: add v2 stack (backend, runner, ui-v2) with release workflow

- backend/: Go API server and runner binaries with PocketBase + MinIO storage
- ui-v2/: SvelteKit frontend rewrite
- docker-compose-new.yml: compose file for the v2 stack
- .gitea/workflows/release-v2.yaml: CI/CD for backend, runner, and ui-v2 Docker Hub images
- scripts/pb-init.sh: migrate from wget to curl, add superuser bootstrap for fresh installs
- .env.example: document DOCKER_BUILDKIT=1 for Colima users

ui-v2/Dockerfile

@@ -0,0 +1,39 @@
+# syntax=docker/dockerfile:1
+FROM node:22-alpine AS builder
+WORKDIR /app
+
+# Install dependencies in a separate layer so it is cached as long as
+# package-lock.json does not change.  The npm cache mount persists the
+# ~/.npm cache across builds so packages are not re-downloaded.
+COPY package.json package-lock.json ./
+RUN --mount=type=cache,target=/root/.npm \
+    npm ci
+
+COPY . .
+
+# Build-time version info — injected by docker-compose or CI via --build-arg.
+ARG BUILD_VERSION=dev
+ARG BUILD_COMMIT=unknown
+
+# Expose as PUBLIC_ env vars so SvelteKit's $env/dynamic/public can read them.
+ENV PUBLIC_BUILD_VERSION=$BUILD_VERSION
+ENV PUBLIC_BUILD_COMMIT=$BUILD_COMMIT
+
+RUN npm run build
+
+# ── Runtime image ──────────────────────────────────────────────────────────────
+# adapter-node bundles all server-side dependencies into build/ — no npm install
+# needed at runtime.  We do need package.json (for "type": "module") so Node
+# resolves the ESM output correctly when there is no parent package.json.
+FROM node:22-alpine
+WORKDIR /app
+
+COPY --from=builder /app/build ./build
+COPY --from=builder /app/package.json ./package.json
+
+ENV NODE_ENV=production
+ENV PORT=3000
+ENV HOST=0.0.0.0
+
+EXPOSE $PORT
+CMD ["node", "build"]