Use existing en.json i18n keys for guest policy notifications; resolve nested keys on frontend

[Copilot]

The guest policy change notification was hardcoding English strings in Akka ("Ask moderator", "Always accept", etc.) as messageValues, making them untranslatable and duplicating app.guest-policy.button.* keys already in en.json.

Changes

• SetGuestPolicyMsgHdlr.scala: Pass the i18n key ("app.guest-policy.button.askModerator" etc.) as messageValues["0"] instead of a hardcoded English label. Use Option[String] to eliminate the empty-string sentinel pattern.

• notifications/component.tsx: Add useIntl() and a resolveMessageValues helper — any messageValue starting with "app." is resolved via intl.formatMessage({ id: v }) before being passed to <FormattedMessage>, enabling full client-locale translation of nested i18n keys sent from the server.

const resolveMessageValues = (
  messageValues: Record<string, string>,
): Record<string, string> => Object.fromEntries(
  Object.entries(messageValues).map(([k, v]) => [
    k,
    typeof v === 'string' && v.startsWith('app.') ? intl.formatMessage({ id: v }) : v,
  ]),
);

• en.json: Add missing "app.guest-policy.button.alwaysAcceptAuth": "Always accept authenticated" key (used by the ALWAYS_ACCEPT_AUTH policy type, previously had no corresponding entry).

• lockViewers.ts (tests): Improve all three presentation permission tests to also assert the correct toast notification fires:

  • presenterPolicyModeratorOnly → asserts "Presenter request is now disabled for viewers"
  • presenterPolicyRequireApproval / presenterPolicyFreeForAll → first set moderatorOnly to enter a state where switching away triggers the "Presenter request is now enabled for viewers" notification, then assert it appears

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