fix(themes/powerline): restore POWERLINE_PROMPT_FOREGROUND_COLOR support

The cleanup in #2360 overwrote the fix from #2231, causing
POWERLINE_PROMPT_FOREGROUND_COLOR to be ignored. Restore the variable
with a safe default of '-' (no override) so existing setups are
unaffected while still allowing foreground color customization.

Fixes #2374

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: seefood

themes/powerline-plain/powerline-plain.base.bash

@@ -26,7 +26,7 @@ function __powerline_left_segment {
 		fi
 	fi
 
-	LEFT_PROMPT+="$(set_color - "${params[1]}")${pad_before_segment}${params[0]}${normal?}"
+	LEFT_PROMPT+="$(set_color "${POWERLINE_PROMPT_FOREGROUND_COLOR:--}" "${params[1]}")${pad_before_segment}${params[0]}${normal?}"
 	LAST_SEGMENT_COLOR=${params[1]}
 	((SEGMENTS_AT_LEFT += 1))
 }

themes/powerline/powerline.base.bash

@@ -268,8 +268,8 @@ function __powerline_left_segment() {
 		fi
 	fi
 
-	#change here to cahnge fg color
-	LEFT_PROMPT+="$(set_color - "${params[1]:-}")${pad_before_segment}${params[0]}${normal?}"
+	#change here to change fg color
+	LEFT_PROMPT+="$(set_color "${POWERLINE_PROMPT_FOREGROUND_COLOR:--}" "${params[1]:-}")${pad_before_segment}${params[0]}${normal?}"
 	#seperator char color == current bg
 	LAST_SEGMENT_COLOR="${params[1]:-}"
 	((SEGMENTS_AT_LEFT += 1))