fix: enforce PDF operation history retention

[mberrys]

Summary

Closes #32. The canonical operation-history chain, artifact store, rollback, and retention implementation were already present on dev; the remaining production gap was that no workflow invoked retention enforcement. This change applies the existing configured policy after accepted outputs in PdfTool repair, Action List, add-bleed, and Editor rollback flows. The immutable history event and output stay recorded if a retention sweep fails, and the workflow reports the failure.

Changes

• Invoke enforceRetention() after accepted output or rollback events in the production paths above.
• Document enforcement behavior and add the required changelog and architecture evidence manifests.

Verification

• scripts/agent/check-architecture.py --base origin/dev --head HEAD — passed.
• scripts/agent/check-change.py --base origin/dev — source integrity, architecture catalog, generated adapters, preflight truth, QML parity, search and independent validation gates, Qt runtime wiring, and clang-format passed. Overall result is incomplete/failing because this isolated worktree has no configured build directory; mapped builds and focused tests could not run. No configure was run.
• Manual inspection confirmed the retention API had no production callers before this change.

Hosted CI should provide the missing compile and test proof.

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