refactor: replace custom escapeHtml with Hono's html template

Hono's `html` tagged template auto-escapes all interpolated values;
`raw()` is used for the email body which must render as HTML.
This removes the ad-hoc utility and aligns entries.ts with the
same pattern already used in admin.ts.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

src/utils/html.ts

@@ -1,7 +0,0 @@
-export function escapeHtml(str: string): string {
-  return str
-    .replace(/&/g, "&")
-    .replace(/</g, "&lt;")
-    .replace(/>/g, "&gt;")
-    .replace(/"/g, "&quot;");
-}