fix: pass Vite env vars as build args in Dockerfile

Vite needs VITE_ZITADEL_ISSUER and VITE_ZITADEL_CLIENT_ID at build time
for the frontend bundle.

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

Dockerfile

@@ -4,6 +4,10 @@ WORKDIR /app
 COPY frontend/package.json frontend/bun.lock* ./
 RUN bun install --frozen-lockfile || bun install
 COPY frontend/ .
+ARG VITE_ZITADEL_ISSUER=https://auth.kuns.dev
+ARG VITE_ZITADEL_CLIENT_ID
+ENV VITE_ZITADEL_ISSUER=$VITE_ZITADEL_ISSUER
+ENV VITE_ZITADEL_CLIENT_ID=$VITE_ZITADEL_CLIENT_ID
 RUN bun run build
 
 # Stage 2: Build backend