add interactive keyboard viewer, fix parser, move spec PDF

interactive layout viewer with version tabs, modifier key highlighting,
dead key compositions, ISO enter spanning two rows, arrow cluster.
fix keylayout parser mapSet range handling, update PDF build scripts,
move eurkey-layout-complete.pdf to spec/.

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

scripts/build-pdf.sh

@@ -1,8 +1,10 @@
 #!/usr/bin/env bash
 # Generate keyboard layout PDFs from .keylayout files.
-# Requires: fpdf2 (pip install fpdf2)
 set -euo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 
+# auto-install Python dependencies
+python3 -c "import fpdf" 2>/dev/null || pip3 install --quiet fpdf2
+
 exec python3 "${SCRIPT_DIR}/generate_layout_pdf.py" "$@"