Migrate Process-PSModule documentation source of truth into Process-PSModule

[MariusStorhaug]

Parent: #423
Blocked by: #425

Process-PSModule documentation currently spread across repositories should be consolidated into Process-PSModule as the source of truth.

Request

Move relevant docs content from PSModule/docs into Process-PSModule and update references so behavior documentation lives next to workflows/actions.

Acceptance criteria

• Source-of-truth Process-PSModule docs exist in Process-PSModule.
• Existing links in module repos and templates point to Process-PSModule docs.
• Duplicated/superseded docs in PSModule/docs are replaced with deprecation pointers.

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Technical decisions

Proximity model: Keep behavior documentation co-located with implementation.

Compatibility: Preserve or redirect critical links used by existing repositories.

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Implementation plan

• Define target docs structure in Process-PSModule
• Migrate prioritized Process-PSModule docs pages
• Update cross-repo links/references
• Validate docs build and navigation
• Publish migration mapping in parent Consolidate PSModule documentation into Process-PSModule and retire PSModule/docs #423