[#70480] Remove unused `ConfirmDialogService` form augmentation, `ConfirmationDialogHelper`

[myabc]

Ticket

https://community.openproject.org/wp/70480

This pull request removes the unused ConfirmationDialogHelper Ruby module and simplifies the Angular ConfirmDialogService by eliminating legacy Rails form augmentation logic.

Code cleanup and modernization:

• Removed the entire ConfirmationDialogHelper Ruby module, which was previously used to render confirmation dialogs for Rails forms but is now obsolete.
• In ConfirmDialogService (confirm-dialog.service.ts), removed the logic for listening to Rails form submissions and augmenting them with confirmation dialogs, as this integration is no longer needed. [1] [2]
• Switched to using Angular's inject function for dependency injection in ConfirmDialogService, further simplifying the service.
• Improved error handling in the confirm method by rejecting with an Error object when the dialog is cancelled, instead of a bare rejection.

Screenshots

There should be no visual changes.

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Merge checklist

• [ ] Added/updated tests
• [ ] Added/updated documentation in Lookbook (patterns, previews, etc)
• [ ] Tested major browsers (Chrome, Firefox, Edge, ...)

[github-actions[bot]]

[!CAUTION] The provided work package version does not match the core version

Details:

• Work package URL: https://community.openproject.org/wp/70480
• Work package version: not set
• Core version: 17.1.0

Please make sure that:

• The work package version OR your pull request target branch is correct