Fix : more messaging flow issues

[HarshMN2345]

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Summary by CodeRabbit

• New Features

  • Custom filters mode for providers and topics (new header prop)
  • Confirm-exit prompt enabled on provider creation wizard

• Bug Fixes

  • Prevented unwanted interactions in image preview links (click/mousedown)
  • Adjusted popover alignment in message/provider creation
  • Modal description slot rendering fixed
  • Replaced empty-search UI for targets with a card-based empty state

• Refactor

  • Topics modal API changed to onUpdate/selected (event dispatch replaced)

• Style

  • "Add subscriber" → "Create subscriber"
  • Search placeholder refined to "Search by type or ID"

• Content

  • Success message updated to "created" after adding subscribers

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