TUI: mouse drag selection with OSC 52 copy; Markdown emphasis follows CommonMark; v0.5.0

- Drag, double-click (word) and triple-click (line) selection in the log,
  auto-scroll at the edges, soft-wrapped lines joined on copy.
- sashidown ANSI renderer: delimiter runs with flanking rules, so
  intraword underscores (test_apply_patch.c) stay literal; unmatched
  * _ and backticks are shown as-is; * and _ do not close each other.
- tests: test_textsel, test_markdown.

Makefile

@@ -80,7 +80,7 @@ CORE_SRC = \
 	src/models.c \
 	src/metrics.c
 
-SRC = $(CORE_SRC) src/tui.c src/main.c
+SRC = $(CORE_SRC) src/textsel.c src/tui.c src/main.c
 OBJ = $(SRC:.c=.o)
 HDRS = $(wildcard include/*.h) $(wildcard src/tools/*.h) $(CJSON_DIR)/cJSON.h
 
@@ -104,6 +104,8 @@ TESTS = \
 	tests/test_models \
 	tests/test_sandbox \
 	tests/test_keymap \
+	tests/test_textsel \
+	tests/test_markdown \
 	tests/test_shell_compact \
 	tests/test_skills \
 	tests/test_plugins \
@@ -161,6 +163,12 @@ tests/test_replay_real: tests/test_replay_real.c src/ctl_parse.c src/json_baseli
 tests/test_mm_tool: tests/test_mm_tool.c src/mm_tool.c include/mm_tool.h
 	$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ tests/test_mm_tool.c src/mm_tool.c
 
+tests/test_textsel: tests/test_textsel.c src/textsel.c include/cst_textsel.h
+	$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ tests/test_textsel.c src/textsel.c
+
+tests/test_markdown: tests/test_markdown.c $(SD_DIR)/libsashidown.a
+	$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ tests/test_markdown.c $(LDFLAGS) -lsashidown -lm
+
 tests/test_%: tests/test_%.c $(CORE_SRC) $(HDRS)
 	$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ $< $(CORE_SRC) $(TEST_LIBS)