Fix — Comment Overflow + Reply Threading

What Was Fixed

Comment entries and form elements were bleeding beyond their container boundaries
Added overflow: hidden; box-sizing: border-box to .comment-entry
Added min-width: 0 on flex children to prevent textarea overflow
Added flex-shrink: 0 on buttons to prevent button collapse
Comment form now properly contained within section boundaries

Reply button on every comment — click to open inline reply form
One level only: users can reply to comments but not to replies (no infinite nesting)
Threaded display: replies indented with left border (border-left: 2px solid #333)
Firestore subcollection: replies stored at comments/{section}/entries/{commentId}/replies/{replyId}
Security rules updated: allow read, create: if true on replies subcollection
Reply rendering: each comment fetches its replies, renders inline below the comment

match /comments/{section}/entries/{entry} — read, create, update (name-verified)
match /{document=**} — deny all

match /comments/{section}/entries/{entry} — read, create, update (name-verified)
match /comments/{section}/entries/{entry}/replies/{reply} — read, create
match /{document=**} — deny all

index.html — CSS overflow fixes, reply CSS, complete comment engine rewrite with reply support
Firestore security rules — deployed via Firebase Rules API