chore: truncate leftover participant and event names

Stefan Latsarevichrequested to merge
s.latsarevich/k3k-web-frontend:3333-truncate-participant-name-follow-up into main

Following up on merge request 3371, which addresses missing participant name truncations and a few event title truncations.

Closes opentalk/product/tickets#187 (closed)

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