Align daily update issue workflow with canonical prompt and date-based title

[Copilot]

This issue requires daily update issues to use a standardized prompt, enforce 2026/date-scoped research guidance, and include strict topStories.sourceUrl citation rules. The workflow now emits that exact prompt and uses the required Update DD.MM.YYYY title format.

• Workflow output alignment

  • Replaced the generated issue body in .github/workflows/create-update-issue.yml with the canonical “Daily update prompt” content from the issue.
  • Preserved all required guidance blocks:
    • RPI process and cross-surface KPI consistency checks
    • 2026-only + issue-date-prioritized research constraint
    • 10-day retention rule for historical and topStories
    • ARCHIVE.json overflow guidance
    • mandatory sourceUrl direct-primary-source citation requirement

• Issue naming contract

  • Updated title generation from [$TODAY] ... to Update $TODAY_ISSUE.
  • Added TODAY_ISSUE=$(date -u +"%d.%m.%Y") to match the required date format.

• Resulting behavior (snippet)

  run: |
    TODAY_ISSUE=$(date -u +"%d.%m.%Y")
    gh issue create \
      --repo "$REPO" \
      --title "Update $TODAY_ISSUE" \
      --body "$BODY" \
      --assignee "copilot"