feat: visually indicate normal vs insert

src/sh/theme.sh

@@ -18,6 +18,8 @@ FORMAT_CURRENT="${FORMAT_CURRENT:-"👉"}"
 SEARCH_PROMPT=${SEARCH_PROMPT:-"🔎 〉"}
 ARTIST_PROMPT="${ARTIST_PROMPT:-"🎤 ${CARTIST}%s$OFF 〉"}"
 FULL_PROMPT="${FULL_PROMPT:-"🎤 ${CARTIST}%s$OFF 》${CTITLE}%s$OFF 〉"}"
+PROMPT_NORMAL="${PROMPT_NORMAL:-"[n]"}"
+PROMPT_INSERT="${PROMPT_INSERT:-"[i]"}"
 
 # Artist view
 AV_PERSON="${AV_PERSON:-"🧑‍🎤 $CARTIST<<name>>$OFF"}"