Add Scenario catalog and launch

[Roman Lutz (romanlutz)]

Summary

Adds registered Scenario discovery, target and technique configuration, dataset and baseline selection, authoritative launch previews, and run creation. The post-launch handoff remains intentionally small because live monitoring arrives in the next layer.

What this layer adds

• Searchable registered Scenario catalog and details.
• Target, technique, dataset, baseline, and Scenario-parameter configuration.
• Backend-authoritative launch preview and validation.
• Run creation and navigation into the Scenario workflow.

Preview

Stack

This is 2 of 7 in the Scenario GUI dependent PR stack and depends on #2372.

Layer	Scope	Pull request
1	Progress foundation	#2372
2	Catalog and launch (this PR)	#2373
3	Live progress	#2374
4	Run history	#2375
5	FIFO scheduling	#2376
6	Configuration sizing	#2377
7	Result details	#2378

See the full implementation, screenshots, walkthrough, validation, and operational notes.

Validation

• Backend: 15,212 passed, 120 skipped.
• Frontend: 68/68 suites, 1,286/1,286 tests; lint, TypeScript, and production build passed.
• Mock E2E, retries disabled: 91 passed, 0 failed, 0 skipped.
• Seeded E2E, retries disabled: 62 passed, 0 failed, 0 skipped.
• All configured pre-commit hooks passed; distinguished-engineer review approved the final stack.