refactor(pdf-compress): replace Ghostscript with qpdf + iLovePDF API

Ghostscript -sDEVICE=pdfwrite fundamentally re-encodes fonts, causing
garbled text regardless of parameters. This cannot be fixed.

New approach:
- Local: qpdf-only lossless structural optimization (5-30% savings,
  zero corruption risk — fonts and images completely untouched)
- Cloud: iLovePDF API integration (auth → start → upload → process →
  download) with 3 levels (recommended/extreme/low), proper image
  recompression without font corruption

Frontend: 3 modes (cloud recommended, cloud extreme, local lossless).
Docker: ILOVEPDF_PUBLIC_KEY env var added.

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

docker-compose.yml

@@ -44,6 +44,8 @@ services:
       # eTerra ANCPI (parcel-sync module)
       - ETERRA_USERNAME=${ETERRA_USERNAME:-}
       - ETERRA_PASSWORD=${ETERRA_PASSWORD:-}
+      # iLovePDF cloud compression (free: 250 files/month)
+      - ILOVEPDF_PUBLIC_KEY=${ILOVEPDF_PUBLIC_KEY:-}
       # DWG-to-DXF sidecar
       - DWG2DXF_URL=http://dwg2dxf:5001
       # Email notifications (Brevo SMTP)