[swarnendusahu10-dotcom]

Description

Resolves #1287

Prevents the member mention autocomplete popup from firing and intercepting keystrokes when typing an email address or web domain (e.g. contact admin @example.com, @gmail.com, or @company.io).

---

Problem & Background

1. Unwanted Popup on Email/Domain Typing:
   Whenever @ is typed after a space, EmbeddedChat enters mention-reading mode. If the user is typing an email address or domain, the popup appears and flickers against partial substring matches of room members.
2. Enter Key Hijacking:
   Because the popup is active in the background, pressing Enter to send the message intercepts the keypress. Instead of sending the email text, it auto-completes whichever random member happened to be highlighted (e.g. replacing @example.com with @Alexandre ), corrupting the user's message.
3. Flaw of Previous Attempt (PR fix: resolve email mention trigger and paginate member list retrieval #1304):
   A previous attempt in PR fix: resolve email mention trigger and paginate member list retrieval #1304 tried to unconditionally disable mentions whenever a dot (.) was present. This was rejected because Rocket.Chat usernames explicitly support dots (e.g. @john.doe), which broke legitimate user mentions.

---

Solution

• Universal Domain Detection via Dot (.): Rather than maintaining a brittle, hardcoded list of 1,500+ top-level domains (.com, .org, .net, .io, .edu, etc.), any email or domain query universally contains a dot separator (.).
• Instant Dismissal & Disarming: The instant a dot is typed in a domain pattern (e.g. @example.), the hook checks if any room member matches. If no member matches (!isValidUsername), it immediately closes the popup (setShowMembersList(false)), clears filteredMembers, and resets mentionIndex to -1.
• Restores Enter Behavior: By disarming the mention index, pressing Enter cleanly sends the message with the email text intact instead of inserting an unwanted member.
• Preserves Dot Usernames: If a teammate actually has a dot in their username (e.g. @john.doe), isValidUsername evaluates to true, so suggestions remain visible and selectable.
• Typo Recovery: Supports backspacing out of typos without prematurely destroying mention state.

---

Changes Made

• Modified packages/react/src/hooks/useSearchMentionUser.js:

  if (query.includes('.') && !isValidUsername) {
    setShowMembersList(false);
    setFilteredMembers([]);
    setMentionIndex(-1);
    return;
  }