feat(results): add audit metadata to results endpoint - #56

Closes #38

Summary

Adds an audit-friendly metadata object to the GET /api/results/:ballotId response, alongside a simple resultsByLabel map ({ "Option A": 45 }) matching the issue's example. Frontend now displays this metadata on the public results page.

Changes

• backend/src/routes/results.ts — added metadata object (ballot_id, ballot_title, total_votes, tally_timestamp, stellar_transaction_id, is_consistent, encryption_note) and resultsByLabel
• backend/src/tests/results.test.ts — coverage for metadata fields and accuracy
• frontend/src/pages/ResultsPage.tsx — displays metadata, consistency badge, collapsible encryption note, Stellar transaction link
• frontend/src/types/index.ts — updated types for the new response shape

Note for reviewers

While rebasing onto the latest main, I found that backend/src/services/emailService.ts and backend/src/routes/votes.ts currently fail to compile with tsc (missing closing brace before the sendVoterTokenEmail doc comment, and a mismatched try/catch block). This is unrelated to this PR — confirmed present directly on main via git show app-upstream/main:... before any of my changes. It will block builds/CI for this and other open PRs until fixed. Flagging here rather than bundling an unrelated fix into this PR.