Complete proxy vote deduplication and preserve queued vote IDs

[BenCodez]

Summary

• deduplicate proxy offline/online cache entries by voteId without relying on vote delay
• standardize persisted JSON on VoteId while retaining compatibility with legacy VoteID
• preserve vote identity through the time-change queue and its JSON/SQL storage
• add a nullable voteId SQL column using a database-compatible probe-and-migrate path
• retain compatibility with older queued votes that do not contain an ID
• add regression coverage for cache deduplication, legacy keys, distinct/null IDs, and queued vote persistence

Why

PRs #1528 and #1529 were stacked on intermediate feature branches. Merging them did not put their net changes onto master. This consolidation PR sits directly on current master and contains the remaining work after #1527.

Impact

Duplicate proxy deliveries with the same explicit vote ID are rejected before caching, and delayed votes retain the same identity when later processed. Legacy cache and queue records continue to load.

Validation

The branch is one commit directly ahead of current master, is automatically mergeable, and includes focused JUnit regression tests. GitHub Actions reruns after each force-update to verify the final squashed commit.