Scaffolding: ZMK module structure, Kconfig, DTS, behavior driver

- zephyr/module.yml with dts_root for dt-bindings
- Kconfig: STENO_ENGINE, dict selection (Plover/Lapwing/test),
  MPHF toggle, Unicode modes, history size, multi-stroke timeout
- DTS behavior binding (one_param, steno key index)
- behavior_steno.c: chord accumulation, all-up detection,
  multi-stroke buffering with timeout, star undo, formatter pipeline,
  3-way dict dispatch (split/MPHF/simple trie)
- dict_embed.S: .incbin from generated header path
- steno_keys.h: 23-key layout, bit positions matching compiler

tests/run_tests.sh

@@ -0,0 +1,64 @@
+#!/bin/bash
+# Run MPHF dictionary tests: compile test dict, build C test, execute.
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+ROOT_DIR="$(cd "$SCRIPT_DIR/.." && pwd)"
+BUILD_DIR="$SCRIPT_DIR/build"
+
+mkdir -p "$BUILD_DIR"
+
+echo "=== Step 1: Create test dictionary JSON ==="
+cat > "$BUILD_DIR/test_dict.json" << 'DICTEOF'
+{
+  "S": "is",
+  "T": "it",
+  "THE": "the",
+  "KAT": "cat",
+  "TK": "did",
+  "SKP": "and",
+  "TPOR": "for",
+  "STO": "so",
+  "HAOEU": "hi",
+  "TKOGS": "dogs",
+  "S/T": "{.}",
+  "PHAO*EUP/HRAOEUPB": "my line"
+}
+DICTEOF
+
+echo "=== Step 2: Compile test dictionary ==="
+python3 "$ROOT_DIR/tools/compile_mphf.py" \
+    "$BUILD_DIR/test_dict.json" \
+    "$BUILD_DIR/test_dict.bin" \
+    --stats
+
+echo ""
+echo "=== Step 3: Build C test binary ==="
+cc -O2 -Wall -Wextra -I"$ROOT_DIR/src" \
+    -o "$BUILD_DIR/test_mphf" \
+    "$SCRIPT_DIR/test_mphf.c" \
+    "$ROOT_DIR/src/dict_mphf.c"
+
+echo ""
+echo "=== Step 4: Run tests ==="
+"$BUILD_DIR/test_mphf" "$BUILD_DIR/test_dict.bin"
+
+echo ""
+echo "=== Step 5: Run with larger dict (if Plover available) ==="
+PLOVER="/tmp/plover-main.json"
+if [ -f "$PLOVER" ]; then
+    echo "Compiling 1000-entry subset..."
+    python3 "$ROOT_DIR/tools/compile_mphf.py" \
+        "$PLOVER" \
+        "$BUILD_DIR/plover_1k.bin" \
+        --max-entries 1000 \
+        --stats
+    echo ""
+    echo "Binary size: $(wc -c < "$BUILD_DIR/plover_1k.bin") bytes"
+else
+    echo "Plover dict not found at $PLOVER, skipping large dict test"
+    echo "Download: curl -sL 'https://raw.githubusercontent.com/openstenoproject/plover/main/plover/assets/main.json' -o /tmp/plover-main.json"
+fi
+
+echo ""
+echo "=== Done ==="