feat(dwg): DWG→DXF via sidecar microservice (libredwg)

Add dedicated dwg2dxf container (Debian slim + libredwg-tools + Flask)
instead of modifying the Alpine base image. The ArchiTools API route
proxies to the sidecar over Docker internal network.

- dwg2dxf-api/: Dockerfile + Flask app (POST /convert, GET /health)
- docker-compose.yml: dwg2dxf service, healthcheck, depends_on
- route.ts: rewritten from local exec to HTTP proxy
- .dockerignore: exclude sidecar from main build context

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Dockerfile

@@ -29,7 +29,7 @@ ENV NODE_ENV=production
 
 RUN apk add --no-cache gdal gdal-tools ghostscript qpdf
 
-# Note: DWG→DXF conversion not available in Alpine (libredwg missing)
+# Note: DWG→DXF conversion handled by dwg2dxf sidecar container (see docker-compose.yml)
 
 RUN addgroup --system --gid 1001 nodejs
 RUN adduser --system --uid 1001 nextjs