OKTA-1248798 - Add ITP SSR updates

[brianduffield-okta]

Description:

• What's changed? Updated the Policies and Self-service registration concepts with ITP self-service EA SSR feature.
• Is this PR related to a Monolith release? 2026.10.0

Resolves:

• OKTA-1248798

Vercel Preview Link:

Policies Concept: https://bd-okta-1248798-ssr-for-itp--developer-docs.vercel.app/docs/concepts/policies/#identity-threat-protection-policies

Self-service Registration: https://bd-okta-1248798-ssr-for-itp--developer-docs.vercel.app/docs/concepts/self-service-registration/#use-policies-to-control-ssr-flows

[okta-prod-github-app]

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Article	Total score Required:80	Word and phrases (Brand, terms) Preferred: 80	Correctness (Spelling, grammar) Preferred: 80	Clarity (Readability) Preferred: 80	Inclusive language (+ accesibility) Preferred: 80
✅ packages/@okta/vuepress-site/docs/concepts/policies/index.md	85	78	88	66
✅ packages/@okta/vuepress-site/docs/concepts/self-service-registration/index.md	87	64	94	74

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