fix(jonathan): make compatible with Ghostty shell-integration

The issue is that Ghostty shell-integration tries to parse PS1. How we're
defining it now, the precmd function from Ghostty does not properly read
the newlines, resulting in broken prompts. This doesn't happen if:

- Zsh is reloaded (`omz reload` or `exec zsh`)
- Ghostty shell integration is disabled (`shell-integration = none` in config)

This fix just removes the newlines, and it's enough to fix the integration.

themes/jonathan.zsh-theme

@@ -60,14 +60,7 @@ ZSH_THEME_GIT_PROMPT_UNMERGED="%{$fg[yellow]%} %{%G═%}"
 ZSH_THEME_GIT_PROMPT_UNTRACKED="%{$fg[cyan]%} %{%G✭%}"
 
 # Use extended characters to look nicer if supported.
-if [[ "${TERM_PROGRAM:-}" = ghostty ]]; then
+if [[ "${langinfo[CODESET]}" = UTF-8 ]]; then
-  PR_SET_CHARSET=""
-  PR_HBAR="-"
-  PR_ULCORNER="-"
-  PR_LLCORNER="-"
-  PR_LRCORNER="-"
-  PR_URCORNER="-"
-elif [[ "${langinfo[CODESET]}" = UTF-8 ]]; then
   PR_SET_CHARSET=""
   PR_HBAR="─"
   PR_ULCORNER="┌"
@@ -109,25 +102,11 @@ else
 fi
 
 # Finally, the prompt.
-PROMPT='${PR_SET_CHARSET}${PR_STITLE}${(e)PR_TITLEBAR}\
+PROMPT='${PR_SET_CHARSET}${PR_STITLE}${(e)PR_TITLEBAR}${PR_CYAN}${PR_ULCORNER}${PR_HBAR}${PR_GREY}(${PR_GREEN}%${PR_PWDLEN}<...<%~%<<${PR_GREY})$(virtualenv_prompt_info)$(ruby_prompt_info)$(conda_prompt_info)${PR_CYAN}${PR_HBAR}${PR_HBAR}${(e)PR_FILLBAR}${PR_HBAR}${PR_GREY}(${PR_CYAN}%(!.%SROOT%s.%n)${PR_GREY}@${PR_GREEN}%m:%l${PR_GREY})${PR_CYAN}${PR_HBAR}${PR_URCORNER}
-${PR_CYAN}${PR_ULCORNER}${PR_HBAR}${PR_GREY}(\
+${PR_CYAN}${PR_LLCORNER}${PR_BLUE}${PR_HBAR}(${PR_YELLOW}%D{%H:%M:%S}${PR_LIGHT_BLUE}%{$reset_color%}$(git_prompt_info)$(git_prompt_status)${PR_BLUE})${PR_CYAN}${PR_HBAR}${PR_HBAR}>${PR_NO_COLOUR} '
-${PR_GREEN}%${PR_PWDLEN}<...<%~%<<\
-${PR_GREY})$(virtualenv_prompt_info)$(ruby_prompt_info)$(conda_prompt_info)${PR_CYAN}${PR_HBAR}${PR_HBAR}${(e)PR_FILLBAR}${PR_HBAR}${PR_GREY}(\
-${PR_CYAN}%(!.%SROOT%s.%n)${PR_GREY}@${PR_GREEN}%m:%l\
-${PR_GREY})${PR_CYAN}${PR_HBAR}${PR_URCORNER}\
-
-${PR_CYAN}${PR_LLCORNER}${PR_BLUE}${PR_HBAR}(\
-${PR_YELLOW}%D{%H:%M:%S}\
-${PR_LIGHT_BLUE}%{$reset_color%}$(git_prompt_info)$(git_prompt_status)${PR_BLUE})${PR_CYAN}${PR_HBAR}\
-${PR_HBAR}\
->${PR_NO_COLOUR} '
 
 # display exitcode on the right when > 0
 return_code="%(?..%{$fg[red]%}%? ↵ %{$reset_color%})"
-RPROMPT=' $return_code${PR_CYAN}${PR_HBAR}${PR_BLUE}${PR_HBAR}\
+RPROMPT=' $return_code${PR_CYAN}${PR_HBAR}${PR_BLUE}${PR_HBAR}(${PR_YELLOW}%D{%a,%b%d}${PR_BLUE})${PR_HBAR}${PR_CYAN}${PR_LRCORNER}${PR_NO_COLOUR}'
-(${PR_YELLOW}%D{%a,%b%d}${PR_BLUE})${PR_HBAR}${PR_CYAN}${PR_LRCORNER}${PR_NO_COLOUR}'
 
-PS2='${PR_CYAN}${PR_HBAR}\
+PS2='${PR_CYAN}${PR_HBAR}${PR_BLUE}${PR_HBAR}(${PR_LIGHT_GREEN}%_${PR_BLUE})${PR_HBAR}${PR_CYAN}${PR_HBAR}${PR_NO_COLOUR} '
-${PR_BLUE}${PR_HBAR}(\
-${PR_LIGHT_GREEN}%_${PR_BLUE})${PR_HBAR}\
-${PR_CYAN}${PR_HBAR}${PR_NO_COLOUR} '