Fix vote percentages when proposal vote counts are sparse

[ManhND226677]

Summary

• calculate proposal vote total from the vote_counts entries that are actually present
• avoid crashing older proposals that do not include every vote type in vote_counts
• return 0.00% when there is no available total vote weight

Fixes #184.

Verification

• npm run lint -- --fix-dry-run (passes with existing repository warnings)
• npm run build (fails in this local environment because node-sass@4.14.1 does not support Node v24 runtime 137; the repo requires Node 14.21.3)

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