Add HTML email templates for magic link sign-in

Extract inline email body into separate Jinja2 templates
(_email/magic_link.html and .txt) with a styled sign-in
button and fallback plain-text link.

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

bp/auth/services/auth_operations.py

@@ -5,7 +5,7 @@ import secrets
 from datetime import datetime, timedelta, timezone
 from typing import Optional, Tuple
 
-from quart import current_app, request, g
+from quart import current_app, render_template, request, g
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import selectinload
@@ -45,16 +45,12 @@ async def send_magic_email(to_email: str, link_url: str) -> None:
     password = os.getenv("SMTP_PASS")
     mail_from = os.getenv("MAIL_FROM") or "no-reply@example.com"
 
-    subject = "Your sign-in link"
-    body = f"""Hello,
+    site_name = config().get("title", "Rose Ash")
+    subject = f"Your sign-in link — {site_name}"
 
-Click this link to sign in:
-{link_url}
-
-This link will expire in 15 minutes.
-
-If you did not request this, you can ignore this email.
-"""
+    tpl_vars = dict(site_name=site_name, link_url=link_url)
+    text_body = await render_template("_email/magic_link.txt", **tpl_vars)
+    html_body = await render_template("_email/magic_link.html", **tpl_vars)
 
     if not host or not username or not password:
         # Fallback: log to console
@@ -74,7 +70,8 @@ If you did not request this, you can ignore this email.
     msg["From"] = mail_from
     msg["To"] = to_email
     msg["Subject"] = subject
-    msg.set_content(body)
+    msg.set_content(text_body)
+    msg.add_alternative(html_body, subtype="html")
 
     is_secure = port == 465  # implicit TLS if true
     if is_secure: