Add core engine: tarot + astrology reading generator with CLI and i18n

Plain-C, dependency-free engine that produces a personalized daily
Celtic Cross tarot spread and natal-chart/transit astrology reading,
plus a standalone CLI (dist/deck-engine) and run.sh wrapper. Includes
English/German output via a simple key=value translation format, and
docs/diagrams describing the architecture and I/O.

engine/Makefile

@@ -0,0 +1,74 @@
+CC      ?= cc
+CFLAGS  ?= -std=c99 -Wall -Wextra -O2
+LDLIBS  := -lm
+
+SRC_DIR       := src
+THIRD_PARTY   := third_party/astronomy/astronomy.c
+TEST_DIR      := tests
+BUILD_DIR     := build
+OBJ_DIR       := $(BUILD_DIR)/obj
+
+# Final build output lives in dist/, next to (not inside) engine/ and res/.
+DIST_DIR      := ../dist
+DIST_IMG_DIR  := $(DIST_DIR)/img
+DIST_I18N_DIR := $(DIST_DIR)/i18n
+RES_IMG_DIR   := ../res/img
+I18N_DIR      := i18n
+SCRIPTS_DIR   := scripts
+
+# Engine logic shared by the CLI and the test binary (no main()).
+ENGINE_SRCS := $(SRC_DIR)/rng.c $(SRC_DIR)/tarot.c $(SRC_DIR)/tarot_data.c \
+               $(SRC_DIR)/astro.c $(SRC_DIR)/reading.c $(SRC_DIR)/i18n.c $(THIRD_PARTY)
+ENGINE_OBJS := $(patsubst %.c,$(OBJ_DIR)/%.o,$(ENGINE_SRCS))
+
+MAIN_OBJ    := $(OBJ_DIR)/$(SRC_DIR)/main.o
+TEST_OBJ    := $(OBJ_DIR)/$(TEST_DIR)/smoke_test.o
+
+BINARY      := $(DIST_DIR)/deck-engine
+TEST_BINARY := $(BUILD_DIR)/smoke_test
+
+.PHONY: all test clean images scripts i18n
+
+all: $(BINARY) images scripts i18n
+
+$(BINARY): $(ENGINE_OBJS) $(MAIN_OBJ)
+	@mkdir -p $(DIST_DIR)
+	$(CC) $(CFLAGS) -o $@ $^ $(LDLIBS)
+
+# The HTML report expects card art at img/<file> next to the binary, so
+# every build refreshes a copy alongside it (cheap: 22 small JPEGs).
+images:
+	@mkdir -p $(DIST_IMG_DIR)
+	cp $(RES_IMG_DIR)/*.jpeg $(DIST_IMG_DIR)/
+
+# The CLI expects translation files at i18n/<lang>.lang next to the
+# binary (default --i18n-dir), so every build refreshes a copy alongside
+# it, same as images/. Add a new language by dropping another <code>.lang
+# file into engine/i18n/ - no code or Makefile change needed.
+i18n:
+	@mkdir -p $(DIST_I18N_DIR)
+	cp $(I18N_DIR)/*.lang $(DIST_I18N_DIR)/
+
+# run.sh is refreshed every build. user.properties is only seeded once
+# (from the placeholder template) so a rebuild never clobbers the user's
+# own filled-in birth data.
+scripts:
+	@mkdir -p $(DIST_DIR)
+	cp $(SCRIPTS_DIR)/run.sh $(DIST_DIR)/run.sh
+	chmod +x $(DIST_DIR)/run.sh
+	test -f $(DIST_DIR)/user.properties || \
+		cp $(SCRIPTS_DIR)/user.properties.template $(DIST_DIR)/user.properties
+
+test: $(TEST_BINARY)
+	./$(TEST_BINARY)
+
+$(TEST_BINARY): $(ENGINE_OBJS) $(TEST_OBJ)
+	$(CC) $(CFLAGS) -o $@ $^ $(LDLIBS)
+
+$(OBJ_DIR)/%.o: %.c
+	@mkdir -p $(dir $@)
+	$(CC) $(CFLAGS) -c -o $@ $<
+
+clean:
+	rm -rf $(BUILD_DIR) $(BINARY) $(DIST_IMG_DIR) $(DIST_I18N_DIR) $(DIST_DIR)/run.sh
+	# user.properties holds the user's own data - never removed by clean.