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.

CMakeLists.txt

@@ -80,7 +80,7 @@ set(CST_CORE_SOURCES
 set(CST_SOURCES ${CST_CORE_SOURCES} src/main.c)
 
 if(CST_BUILD_TUI)
-  list(APPEND CST_SOURCES src/tui.c)
+  list(APPEND CST_SOURCES src/textsel.c src/tui.c)
 else()
   list(APPEND CST_SOURCES src/tui_stub.c)
 endif()
@@ -151,9 +151,17 @@ endif()
 # --- tests ---
 enable_testing()
 set(_CST_SMALL_TESTS test_ctl_frontier test_ctl_heredoc test_json_baseline
-    test_replay_starvation test_replay_real test_mm_tool)
+    test_replay_starvation test_replay_real test_mm_tool test_textsel
+    test_markdown)
 foreach(t ${_CST_SMALL_TESTS})
-  if(t STREQUAL test_ctl_frontier OR t STREQUAL test_ctl_heredoc)
+  if(t STREQUAL test_textsel)
+    add_executable(${t} tests/${t}.c src/textsel.c)
+  elseif(t STREQUAL test_markdown)
+    add_executable(${t} tests/${t}.c)
+    target_include_directories(${t} PRIVATE "${SD_DIR}/include")
+    target_link_libraries(${t} PRIVATE "${SASHIDOWN_A}")
+    add_dependencies(${t} sashidown)
+  elseif(t STREQUAL test_ctl_frontier OR t STREQUAL test_ctl_heredoc)
     add_executable(${t} tests/${t}.c src/ctl_parse.c)
   elseif(t STREQUAL test_json_baseline)
     add_executable(${t} tests/${t}.c src/json_baseline.c vendor/cjson/cJSON.c)