feat(ui): make prompt not required

- also change the placeholder text

invokeai/frontend/web/src/features/parameters/components/Parameters/Core/ParamNegativeConditioning.tsx

@@ -20,10 +20,7 @@ const ParamNegativeConditioning = () => {
         name="negativePrompt"
         value={negativePrompt}
         onChange={(e) => dispatch(setNegativePrompt(e.target.value))}
-        placeholder={t('parameters.negativePrompts')}
-        _focusVisible={{
-          borderColor: 'error.600',
-        }}
+        placeholder={t('parameters.negativePromptPlaceholder')}
         fontSize="sm"
         minH={16}
       />

invokeai/frontend/web/src/features/parameters/components/Parameters/Core/ParamPositiveConditioning.tsx

@@ -70,13 +70,11 @@ const ParamPositiveConditioning = () => {
 
   return (
     <Box>
-      <FormControl
-        isInvalid={prompt.length === 0 || Boolean(prompt.match(/^[\s\r\n]+$/))}
-      >
+      <FormControl>
         <IAITextarea
           id="prompt"
           name="prompt"
-          placeholder={t('parameters.promptPlaceholder')}
+          placeholder={t('parameters.positivePromptPlaceholder')}
           value={prompt}
           onChange={handleChangePrompt}
           onKeyDown={handleKeyDown}