fix: create roadmap forks with supported gh flags

[eohjelle]

Summary

• remove the unsupported --remote=false flag from fork creation
• assert the exact supported fork command in the outside-contributor regression test

Root cause and impact

push_target() passed a positional repository together with --remote=false. Current GitHub CLI rejects any explicit --remote flag when a repository argument is present, so contributors without canonical roadmap write access failed before their fork was created.

The corrected invocation, gh repo fork <repository> --clone=false, matches the established fork-creation command used by TauCetiWorker for work on TauCeti.

Validation

• ./tests/run
• successfully created the contributor fork with gh repo fork TauCetiProject/TauCetiProgress --clone=false using GitHub CLI 2.96.0

Closes #8

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