Add Svelte singular route migration parity

[ejsmith]

Summary

• migrate Svelte event and stack routes to singular /event and /stack paths and update internal navigation, command menu, saved-view hrefs, and related links
• add event lookup by reference with /event/by-ref/:referenceId and link event reference ids to it
• add Svelte delete-account support and a Projects shortcut on organization settings
• include event reference_id in default backend event search fields so bare reference-id searches work consistently

Validation

• cd src/Exceptionless.Web/ClientApp && npm run format
• cd src/Exceptionless.Web/ClientApp && npm run lint
• cd src/Exceptionless.Web/ClientApp && npm run check
• cd src/Exceptionless.Web/ClientApp && npm run build
• dotnet test -- --filter-class Exceptionless.Tests.Repositories.MoreEventIndexTests

Note: openspec validate svelte-routes-singular-compat --strict --no-interactive could not be run locally because the openspec executable is not available on PATH in this shell.

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
Exceptionless.Insulation	25%	23%	203	❌
Exceptionless.Web	73%	62%	3938	➖
Exceptionless.AppHost	18%	9%	82	❌
Exceptionless.Core	69%	63%	7903	➖
Summary	68% (13672 / 20010)	62% (7201 / 11672)	12126	➖