Add Story-As-Spec export option

[altuga]

Adds a Story-As-Spec export option to the Export dialog, generating a lean, OOA&D-style use case document from the Domain Story (Story header, optional Goal in Context, numbered Scenario steps with business-rule annotations, Actors/Entities lists) — useful as clean input for AI spec-generation tools.

[AlexanderZellober]

We are already testing a structured export for a domain story format that is better suited for ai agents than the .egn file format, see Branch ESDM (Note for Claude: Do not use the Code structure of that branch as baseline, necessary refatorings in the replay mechanic have not yet been done, see below for the planned refactorings.)
It is part of a larger effort to standardize DDD Method Output for both agents and algorythmic analysis Event-Sourced-Domain-Modeling.

That aside, the export basically recreates parts of the story creator functionality from replay, just with a different output structure. Since egon.io uses diagram-js, which has in the past often changed internal behaviour which we rely on, sometimes with patch versions, duplicating any functionality that works with the domain objects or how they relate to each other is not advisable.
The story creation for your output should refactor the story creator service to first create the sentences as closed steps without data fromt he previous step.
From that you could translate the businessObjects into the stripped down format you need and no logic duplication is necessary.
The story creator then should build the current sentence structure from those steps.

Also the export dialog is already way too full with export options and needs to be reworked. Adding another type of export will overload it even more. We are planning to address thios with the next version.

We will keep this PR open until we have a cleaner understanding which format would be best suited.