Support Discord-style colon emoji shortcuts in meeting chat

## Feature request

Add support for Discord-style emoji shortcuts in chat messages, such as `:smile:`, `:cry:`, or `:thumbsup:`.

## Motivation

Participants want a quick text-based way to insert or render emoticons/emoji in chat, similar to Discord.

## Proposed behavior

- Recognize supported `:emoji_name:` patterns while composing or rendering a chat message.
- Render recognized shortcuts as their corresponding emoji.
- Leave unrecognized shortcuts unchanged as plain text.
- Preserve existing Unicode emoji behavior.

## Acceptance criteria

- A message containing a supported shortcut (for example, `:cry:`) displays the matching emoji.
- Multiple shortcuts in one message are supported.
- Unknown or malformed colon-delimited text is not incorrectly converted.
- The feature works consistently for sent and received chat messages.

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Requested by **Ishaan** during a Conclave meeting.

Start by locating the chat message composer and the sent and received message renderers in the web and mobile clients, then trace how message text is handled. Confirm where supported shortcut names and Unicode emoji behavior should be covered. Done means recognized shortcuts render correctly, multiple shortcuts work, unknown or malformed text remains unchanged, and sent and received messages behave consistently.

Written by the indexing model from the issue text.