Fix #646: Display shortened pubkey instead of 'anon'

[a1denvalu3]

Summary

Fixes #646.

Instead of displaying the generic string "anon" for users who have not yet set a nickname or whose nickname metadata hasn't been received, we now display a shortened version of their public key (e.g., a1b2c3d4...).

Changes

• Updated GeohashRepository.kt:
  • Added formatAnonName helper.
  • Replaced all fallback instances of "anon" with the shortened pubkey.
  • Updated refreshGeohashPeople and display name lookup functions.

Testing

• Verified that geohash participants without nicknames appear as abcd1234... in the list.
• Verified that the user's own name falls back correctly if empty.

[marcorizzo97]

Thank you for taking my request into consideration and fixing that "kind" of bug too.