Phase 3b: working dict compiler + dict download script

- compile_dict.py: full JSC4 binary compiler for compact map dicts.
  Parses Plover JSON → builds hash maps with CRC32 probing →
  produces binary with correct header, pointers, text block, timestamps.
  Tested with small dict — magic + timestamp validation passes.
- download_dicts.sh: fetches Plover main.json from openstenoproject/plover
  and Lapwing dicts from aerickt/plover-lapwing-aio.

Usage: python compile_dict.py main.json -o dicts/steno_dict.bin

tools/dict_compiler/download_dicts.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+# Download Plover and Lapwing steno dictionaries from their official repos.
+# Usage: ./download_dicts.sh [plover|lapwing|all] [output_dir]
+
+set -euo pipefail
+
+THEORY="${1:-all}"
+OUTDIR="${2:-./dicts_src}"
+
+mkdir -p "$OUTDIR"
+
+download_plover() {
+  echo "Downloading Plover main.json..."
+  curl -fsSL \
+    "https://raw.githubusercontent.com/openstenoproject/plover/main/plover/assets/main.json" \
+    -o "$OUTDIR/plover-main.json"
+  echo "  $(python3 -c "import json; print(len(json.load(open('$OUTDIR/plover-main.json'))))" 2>/dev/null || echo '?') entries"
+}
+
+download_lapwing() {
+  local BASE="https://raw.githubusercontent.com/aerickt/plover-lapwing-aio/main/plover_lapwing/dictionaries"
+  echo "Downloading Lapwing dictionaries..."
+  for f in lapwing-base lapwing-commands lapwing-numbers; do
+    curl -fsSL "$BASE/$f.json" -o "$OUTDIR/$f.json"
+    echo "  $f.json: $(python3 -c "import json; print(len(json.load(open('$OUTDIR/$f.json'))))" 2>/dev/null || echo '?') entries"
+  done
+}
+
+case "$THEORY" in
+  plover)  download_plover ;;
+  lapwing) download_lapwing ;;
+  all)     download_plover; download_lapwing ;;
+  *)       echo "Usage: $0 [plover|lapwing|all] [output_dir]"; exit 1 ;;
+esac
+
+echo "Done. Dictionaries saved to $OUTDIR/"