Initial CST-Agent: portable Linux/Termux/Windows coding agent.

Vendored sashidown, OpenAI-compatible env (OPENAI_*), and bootstrap scripts.

Co-authored-by: Cursor <cursoragent@cursor.com>

vendor/sashidown/Makefile

@@ -0,0 +1,16 @@
+CC ?= gcc
+CFLAGS ?= -std=c11 -Wall -Wextra -O2 -Iinclude -Isrc
+SRCS = src/fsm.c src/table_stats.c src/line_index.c src/block_scan.c \
+	src/ansi_style.c src/render.c src/render_ansi.c src/render_json.c \
+	src/sashidown.c src/compat_cmark.c src/stream.c
+OBJS = $(SRCS:.c=.o)
+LIB = libsashidown.a
+
+.PHONY: all clean
+all: $(LIB)
+$(LIB): $(OBJS)
+	$(AR) rcs $@ $(OBJS)
+src/%.o: src/%.c
+	$(CC) $(CFLAGS) -c -o $@ $<
+clean:
+	rm -f $(OBJS) $(LIB)