docs(model-roles/apply): fix dead morphllm.com/dashboard link

[sanjibani]

Replaces https://morphllm.com/dashboard (404) with https://morphllm.com/sign-up (200) — the old dashboard URL was retired.

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Summary by cubic

Fixes a dead link in the Apply model docs by replacing Morph’s retired /dashboard URL with the working /sign-up page. This removes a 404 and sends users to the correct sign-up flow.

^{Written for commit dbeaea0. Summary will update on new commits.}

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[cubic-dev-ai]

No issues found across 1 file

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