Closes #200

Description

Previously, the sender was identified by comparing message.sender (a nickname string) to currentUserNickname. This caused issues when the nickname changed, since past messages would then match or not match incorrectly, leading to inconsistent color assignments.

The updated logic compares message.senderPeerID to meshService.myPeerID, which is a unique and stable identifier for the user. This ensures that the correct color (colorScheme.primary) is applied consistently to the user's own messages, regardless of any nickname changes.

Why this matters

• Fixes a bug where changing your nickname would retroactively change the color of your past messages.

• Prevents conflicts where multiple users with the same nickname might get the same sender color.

• Makes message ownership checks more reliable by using a unique ID instead of a mutable nickname.

Screenshots/Screen recordings

Checklist

• I have read the contribution guidelines: https://github.com/permissionlesstech/bitchat-android?tab=readme-ov-file#contributing
• I have performed a self-review of my code

• I have mentioned the corresponding issue and the relevant keyword (e.g., "Closes: #xy") in the description (see https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue)
• If it is a core feature, I have added automated tests