Fix presenter config and interaction duplication

[cromulus]

Summary

• emit window.claperConfig.supportedLocales as raw JSON in the root layout
• make presenter slide URL generation safe when the presentation hash is missing or the deck length is zero
• add interaction duplication in the event manager and reset poll/quiz results when duplicating
• rework new-poll form state to avoid duplicate poll_opts warnings from unsaved options

Testing

• mix test test/claper/presentations_test.exs test/claper/interactions_test.exs test/claper/polls_test.exs

Notes

• PR targets dev from the contributor fork, per the repo contribution instructions.