fix(hub): switch Dockerfile from npm to bun

hub project uses bun.lock, but Dockerfile was using npm install which
resolves dependencies differently. Switched to oven/bun image and
bun install --frozen-lockfile for deterministic builds.

Co-Authored-By: Claude Code <noreply@anthropic.com>

infra/docker/hub.Dockerfile

@@ -1,13 +1,13 @@
 # ── Build stage ──
-FROM node:22-alpine AS builder
+FROM oven/bun:1.2 AS builder
 WORKDIR /app
 COPY apps/hub/package.json apps/hub/bun.lock ./
-RUN npm install --frozen-lockfile
+RUN bun install --frozen-lockfile
 COPY apps/hub .
-RUN npm run build
+RUN bun run build
 
 # ── Runtime ──
-FROM node:22-alpine AS runtime
+FROM oven/bun:1.2 AS runtime
 RUN addgroup -S appgroup && adduser -S appuser -G appgroup
 WORKDIR /app
 COPY --from=builder /app/.next ./.next
@@ -18,4 +18,4 @@ RUN rm -rf .next/cache && chown -R appuser:appgroup .next
 USER appuser
 EXPOSE 3000
 ENV PORT=3000 NODE_ENV=production
-CMD ["npm", "run", "start"]
+CMD ["bun", "run", "start"]