fix: hide unauthorized bounty actions on org bounties page

[moixbot]

Summary

Fixes #238.

Hide Edit Amount and Delete actions on the org bounties page for users who are not authorized to manage bounties.

Root Cause

The backend already rejects unauthorized edit-bounty-amount and delete-bounty events, but the buttons were still rendered for all logged-in users. That created a misleading UI path where users could click actions they were not allowed to perform.

Changes

• render bounty action buttons only when @current_user_role in [:admin, :mod]
• leave existing server-side authorization checks in place

Result

• unauthorized users no longer see admin/mod-only bounty actions
• admins and mods keep the existing edit/delete workflow
• UI behavior now matches backend permissions

Verification

• confirmed the action cell is now role-gated in Org.BountiesLive
• backend authorization logic remains unchanged
• test suite was not run in this environment because Elixir/Mix is not installed here

[CLAassistant]

All committers have signed the CLA.