[Conway] Active DReps are unchanged across an epoch when there are no proposals

**Property:** Active DReps are unchanged across an epoch when there are no proposals

- Catalog id: `conway-epoch-nopropsame-dreps`
- Era: **conway** · STS: **EPOCH**
- Agda module: `Ledger.Conway.Specification.Epoch.Properties.NoPropSameDReps` (anchor: `clm:NoPropSameDReps`)
- Key definitions: `prop≡∅⇒activeDReps-const`
- Status (derived from the Agda): **stated**

Adjacent to #415 but a distinct statement.

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Tracked in `docs/notes/properties.yaml`; see ADR `docs/notes/0001-ledger-property-tracking.md` and the roadmap `docs/notes/ledger-properties-roadmap.md`.
Part of the properties roadmap (umbrella #45).

Start with the Agda module Ledger.Conway.Specification.Epoch.Properties.NoPropSameDReps and the prop≡∅⇒activeDReps-const definition, then read docs/notes/properties.yaml, docs/notes/0001-ledger-property-tracking.md, and docs/notes/ledger-properties-roadmap.md. Confirm the roadmap’s expected action for this stated property and use the project’s existing conventions to determine what completion should update.

Written by the indexing model from the issue text.