refactor: Use hooks to load email css files

Previously email.css files were explicitly picked from hardcoded path
like public/css/email.css for all apps

frappe/email/email_body.py

@@ -292,17 +292,9 @@ def inline_style_in_html(html):
 	'''
 	from premailer import Premailer
 
-	apps = frappe.get_installed_apps()
-
-	# add frappe email css file
-	css_files = ['assets/css/email.css']
-	if 'frappe' in apps:
-		apps.remove('frappe')
-
-	for app in apps:
-		path = 'assets/{0}/css/email.css'.format(app)
-		css_files.append(path)
-
+	# get email css files from hooks
+	css_files = frappe.get_hooks('email_css')
+	css_files = [path.lstrip('/') for path in css_files]
 	css_files = [css_file for css_file in css_files if os.path.exists(os.path.abspath(css_file))]
 
 	p = Premailer(html=html, external_styles=css_files, strip_important=False)
@@ -480,4 +472,4 @@ def sanitize_email_header(str):
 	return str.replace('\r', '').replace('\n', '')
 
 def get_brand_logo(email_account):
-	return email_account.get('brand_logo')
+	return email_account.get('brand_logo')

frappe/hooks.py

@@ -52,6 +52,8 @@ web_include_js = [
 
 web_include_css = []
 
+email_css = ['/assets/frappe/build/scss/email.css']
+
 website_route_rules = [
 	{"from_route": "/blog/<category>", "to_route": "Blog Post"},
 	{"from_route": "/kb/<category>", "to_route": "Help Article"},