Refine checksum-based publish decision model into fixed Process-PSModule behavior

[MariusStorhaug]

Parent: #423
Related: #184

Process-PSModule release/publish decisions should be fixed and artifact-driven rather than repository-configurable path heuristics.

Request

Refine #184 into a concrete design where build/test always run, publish decisions are made from module/docs artifact checksums, and mutable latest checksums are managed by a GitHub App-backed state mechanism.

Acceptance criteria

• ImportantFilePatterns is removed from the decision model for publish gating.
• Build/test stages run regardless of file path changes.
• Publish matrix is defined by checksum differences (module/docs/both/none).
• Module checksum remains the only signal that can drive module version bump behavior.
• State model distinguishes immutable release provenance vs mutable latest baseline.

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Technical decisions

Fixed process contract: Behavior is non-configurable across module repositories.

State split: Immutable checksum evidence on releases; mutable latest baseline for runtime decisions.

Auth model: GitHub App token is the standard mechanism for state writes.

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Implementation plan

• Write final spec in issue body (or linked design doc)
• Define workflow contract and outputs
• Decompose implementation into PR-sized child tasks
• Link implementation tasks back to 🩹 [Patch]: Only create releases when significant changes are detected (module and documentation) #184 and parent Consolidate PSModule documentation into Process-PSModule and retire PSModule/docs #423