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

CMakeLists.txt

@@ -0,0 +1,105 @@
+# Copyright (c) 2024 Afiq Zudin Hadi
+# SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0
+
+if(CONFIG_STENO_ENGINE)
+if(NOT CONFIG_ZMK_SPLIT OR CONFIG_ZMK_SPLIT_ROLE_CENTRAL)
+
+target_sources(app PRIVATE
+    src/behavior_steno.c
+    src/output.c
+    src/formatter.c
+    src/undo.c
+    src/dict_embed.S
+)
+
+if(CONFIG_STENO_DICT_MPHF)
+  target_sources(app PRIVATE src/dict_mphf.c)
+else()
+  target_sources(app PRIVATE src/trie.c)
+endif()
+
+target_include_directories(app PRIVATE
+    include
+    ${CMAKE_CURRENT_SOURCE_DIR}/src
+)
+
+# ── Dictionary source resolution ──
+find_package(Python3 REQUIRED COMPONENTS Interpreter)
+set(STENO_DICT_BIN ${CMAKE_CURRENT_BINARY_DIR}/steno_dict.bin)
+set(STENO_DICTS_DIR ${CMAKE_CURRENT_SOURCE_DIR}/dicts)
+set(STENO_FETCH ${CMAKE_CURRENT_SOURCE_DIR}/tools/fetch_dict.py)
+
+if(CONFIG_STENO_DICT_PLOVER)
+  set(STENO_DICT_NAME "plover")
+  set(STENO_DICT_SRC ${STENO_DICTS_DIR}/plover-main.json)
+elseif(CONFIG_STENO_DICT_LAPWING)
+  set(STENO_DICT_NAME "lapwing")
+  set(STENO_DICT_SRC ${STENO_DICTS_DIR}/lapwing.json)
+else()
+  set(STENO_DICT_SRC ${STENO_DICTS_DIR}/test.json)
+endif()
+
+# Auto-download dict if needed (Plover/Lapwing only)
+if(DEFINED STENO_DICT_NAME AND NOT EXISTS ${STENO_DICT_SRC})
+  message(STATUS "Steno: downloading ${STENO_DICT_NAME} dictionary...")
+  execute_process(
+      COMMAND ${Python3_EXECUTABLE} ${STENO_FETCH}
+          ${STENO_DICT_NAME} ${STENO_DICTS_DIR}
+      RESULT_VARIABLE FETCH_RESULT
+  )
+  if(NOT FETCH_RESULT EQUAL 0)
+    message(WARNING "Steno: dict download failed. Build may fail.")
+  endif()
+endif()
+
+# ── Dictionary compilation ──
+if(EXISTS ${STENO_DICT_SRC})
+  if(CONFIG_STENO_DICT_MPHF)
+    # Fetch at build time if hash changed (re-run on rebuild)
+    if(DEFINED STENO_DICT_NAME)
+      add_custom_command(
+          OUTPUT ${STENO_DICT_SRC}.stamp
+          COMMAND ${Python3_EXECUTABLE} ${STENO_FETCH}
+              ${STENO_DICT_NAME} ${STENO_DICTS_DIR}
+          COMMAND ${CMAKE_COMMAND} -E touch ${STENO_DICT_SRC}.stamp
+          COMMENT "Checking ${STENO_DICT_NAME} dictionary for updates"
+      )
+      add_custom_target(steno_dict_fetch DEPENDS ${STENO_DICT_SRC}.stamp)
+    endif()
+
+    add_custom_command(
+        OUTPUT ${STENO_DICT_BIN}
+        COMMAND ${Python3_EXECUTABLE}
+            ${CMAKE_CURRENT_SOURCE_DIR}/tools/compile_mphf.py
+            ${STENO_DICT_SRC} ${STENO_DICT_BIN}
+            --max-size ${CONFIG_STENO_DICT_MAX_SIZE}
+        DEPENDS ${STENO_DICT_SRC}
+            ${CMAKE_CURRENT_SOURCE_DIR}/tools/compile_mphf.py
+        COMMENT "Compiling steno dictionary (MPHF)"
+    )
+  else()
+    add_custom_command(
+        OUTPUT ${STENO_DICT_BIN}
+        COMMAND ${Python3_EXECUTABLE}
+            ${CMAKE_CURRENT_SOURCE_DIR}/tools/compile_simple.py
+            ${STENO_DICT_SRC} -o ${STENO_DICT_BIN}
+        DEPENDS ${STENO_DICT_SRC}
+            ${CMAKE_CURRENT_SOURCE_DIR}/tools/compile_simple.py
+        COMMENT "Compiling steno dictionary (simple)"
+    )
+  endif()
+
+  add_custom_target(steno_dict_gen DEPENDS ${STENO_DICT_BIN})
+  if(TARGET steno_dict_fetch)
+    add_dependencies(steno_dict_gen steno_dict_fetch)
+  endif()
+  add_dependencies(app steno_dict_gen)
+
+  # Generate header with dict path for .incbin
+  file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/steno_dict_path.h
+       "#define STENO_DICT_BIN_PATH \"${STENO_DICT_BIN}\"\n")
+  target_include_directories(app PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
+endif()
+
+endif() # central role
+endif() # CONFIG_STENO_ENGINE