refactor(ordering): remove priority from all story/task orderBy
Story- en taak-ordering is nu puur sort_order asc (created_at als
tiebreaker). PBI-ordering (priority + sort_order) blijft ongewijzigd.
Gewijzigd: backlog/route, pbis/stories/route, claude-context/route,
next-story/route, workspace/route, tasks/route, sprint-runs (query +
in-memory sort), solo-workspace-server, page.tsx (app + mobile + sprint),
store compareStory, actions/sprints story-query, next-story test.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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