fix: terminate truncated ANSI codes, honor ASCII fallback in box borders

- blk/nln/unbl/rsinv/hid/unh were missing the trailing 'm', producing
  invalid escape sequences. Concatenated with text (e.g. temperature
  readouts using ${blk}), strict-parsing terminals would read the
  digits/letters that followed as CSI parameters, causing garbled
  output or unwanted cursor movement.
- norm used bash's $"..." locale-translation syntax on an ANSI code
  instead of a plain string.
- set-boxtype() always ran box-norm/double/heavy/light/rounded, which
  draw with hardcoded Unicode corner glyphs, even when
  check_unicode_support() determined the terminal/locale couldn't
  render Unicode. This defeated box_chars_simple()'s ASCII fallback
  entirely. Now the Unicode style dispatch is skipped when
  unicode_supported is false.
- Removed a duplicate box-singlechar() definition.

functions

@@ -56,20 +56,20 @@ if [[ "$TERM" != "linux" ]] ; then
   lyl="${ESC}[38;5;228m" # light yellow
   lrd="${ESC}[38;5;196m" # light red
   gry="${ESC}[38;5;240m" # Grey
-  norm=$"${ESC}[39m"  # default/normal                                                                      
+  norm="${ESC}[39m"  # default/normal
   #
   bld="${ESC}[1m"    # bold
   unb="${ESC}[21m"   # un-bold
   dim="${ESC}[2m"    # dim
   und="${ESC}[22m"   # un-dim
   unl="${ESC}[4m"    # underline
-  nln="${ESC}[24"    # not-underline
-  blk="${ESC}[5"     # blinking
-  unbl="${ESC}[25"   # stop blinking
+  nln="${ESC}[24m"   # not-underline
+  blk="${ESC}[5m"    # blinking
+  unbl="${ESC}[25m"  # stop blinking
   inv="${ESC}[7m"    # invert
-  rsinv="${ESC}[27"  # reset http://www.endmemo.com/unicode/unicodeconverter.phpnvert
-  hid="${ESC}[8"     # hidden
-  unh="${ESC}[28"    # unhide
+  rsinv="${ESC}[27m" # reset invert
+  hid="${ESC}[8m"    # hidden
+  unh="${ESC}[28m"   # unhide
   dfl="${ESC}[0m"    # restore default
 fi
 
@@ -98,7 +98,8 @@ box_chars_simple() {
 
 set_box_chars() {
     if check_unicode_support; then
-        case "$OSTYPE" in 
+        unicode_supported=true
+        case "$OSTYPE" in
             linux-gnu*|cygwin|msys)
                 return_arrow=$(echo -e "\u2BAC")
                 enter_arrow=$(echo -e "\u21B5")
@@ -139,6 +140,7 @@ set_box_chars() {
         esac
     else
         # ASCII fallbacks
+        unicode_supported=false
         return_arrow=">"
         enter_arrow="<"
         green_check="+"
@@ -258,28 +260,34 @@ set-boxtype() {
   # Ensure characters are defined
   set_box_chars
   update_terminal_width
-  
+
+  # box-norm/double/heavy/light/rounded all draw with hardcoded Unicode corner
+  # glyphs; on a terminal without Unicode support, box_chars_simple() (called
+  # from set_box_chars above) already set full ASCII borders/corners, so skip
+  # the style dispatch entirely rather than clobbering them.
+  if [[ "$unicode_supported" != true && "$style" != "char" ]]; then
+    return
+  fi
+
   # Set the box style
-  case $style in 
+  case $style in
     norm)   box-norm ;;
     double) box-double ;;
     heavy)  box-heavy ;;
     light)  box-light ;;
     rounded) box-rounded ;;
     char)   box-singlechar ;;
-    *)      
+    *)
       # Handle unknown box types by falling back to normal
       echo "Warning: Unknown box type '$style', falling back to 'norm'" >&2
       boxtype="norm"
-      box-norm 
+      if [[ "$unicode_supported" == true ]]; then
+        box-norm
+      fi
       ;;
   esac
 }
 
- box-singlechar(){
-  set_borders "$borderchar" "$borderchar" "$borderchar" "$borderchar" "$borderchar" "$borderchar" "$borderchar" "$borderchar" "-"
-}
-
 format_boxborder() {
     local alignment="left"
     local box_type="norm"