feat(data-entry): Add unified receipt form with OCR confidence tracking

New unified receipt creation system with:
- UnifiedReceiptForm component with inline OCR preview and confidence indicators
- Compact upload zone with drag-drop and camera support
- TVA and Payment fields with dynamic add/remove
- Supplier dual-field with autocomplete and OCR hint
- Receipt form sections with collapsible auxiliary data

Backend OCR improvements:
- Add confidence_tva and confidence_payment to extraction results
- Update TVA extraction to return confidence scores
- Include TVA (15%) and payment (10%) in overall_confidence calculation

Also includes:
- CSS design system rules documentation
- Port check helper function for service scripts
- Expanded design tokens documentation in CLAUDE.md

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/service-helpers.sh

@@ -134,6 +134,21 @@ check_port_available() {
   fi
 }
 
+# Check if port is in use (opposite of check_port_available)
+# Usage: check_port_in_use <port>
+# Returns 0 if port IS IN USE, 1 if FREE
+check_port_in_use() {
+  local port=$1
+
+  if netstat -tuln 2>/dev/null | grep -q ":${port} " || \
+     ss -tuln 2>/dev/null | grep -q ":${port} " || \
+     lsof -ti:${port} &>/dev/null; then
+    return 0  # Port is in use
+  else
+    return 1  # Port is free
+  fi
+}
+
 # Display a nice header
 # Usage: print_header "Title"
 print_header() {