Tighten PS1 caps and emphasize prompt arrow

- Bold the prompt arrow for stronger line-break emphasis

- Tighten spacing at the right end cap

- Document PS1 design rationale and palette

dotfiles/install/install-global-ps1.sh

@@ -123,18 +123,20 @@ ps1_on() {
   # Status colors
   local OK="\[\e[38;5;76m\]"
   local BAD="\[\e[38;5;203m\]"
+  local BOLD="\[\e[1m\]"
+  local NOBOLD="\[\e[22m\]"
 
   # Separators w/ fallback (NF vs non-NF)
   local SEP_EXPR='\$( [ "$__PS1_USE_NF" -eq 1 ] && printf "" || printf "▶" )'
   local LEFT_EXPR='\$( [ "$__PS1_USE_NF" -eq 1 ] && printf "" || printf "[" )'
   local RIGHT_EXPR='\$( [ "$__PS1_USE_NF" -eq 1 ] && printf "" || printf "]" )'
 
-  local PROMPT_SYM="\$( [ \$__PS1_STATUS -eq 0 ] && printf '${OK}' || printf '${BAD}' )➜${RST}"
+  local PROMPT_SYM="\$( [ \$__PS1_STATUS -eq 0 ] && printf '${OK}' || printf '${BAD}' )${BOLD}➜${NOBOLD}${RST}"
 
   PS1="\
 ${FRAME}╭─${RST}\
 ${Z1_BG}${Z1_FG}${LEFT_EXPR} \d \A \u ${RST}${Z1_BG}${Z2_BG}${Z2_FG}${SEP_EXPR}${RST}\
-${Z2_BG}${Z2_FG} @\h ${PATH_FG}\${__PS1_PATH} ${RST}${Z2_BG}${Z2_FG}${RIGHT_EXPR}${RST}\
+${Z2_BG}${Z2_FG} @\h ${PATH_FG}\${__PS1_PATH}${RST}${Z2_BG}${Z2_FG}${RIGHT_EXPR}${RST}\
 \n${FRAME}╰── ${RST}${PROMPT_SYM} \${__PS1_SYM} "
 }