feat(elections): build elections.us-rse.org to replace ElectionBuddy [epic]

Summary

Build a ranked-choice voting application at elections.us-rse.org that replaces our dependency on ElectionBuddy. The app will live in this repo alongside the marketing site, share the design-system, and support both single-winner (IRV) and multi-winner (STV) races used by US-RSE elections.

Goals

• Eliminate recurring ElectionBuddy cost and give US-RSE full control over the election platform.
• Support ranked-choice voting (IRV for single seats, STV for multi-seat board elections).
• Preserve ballot secrecy: voter identity is separated from the submitted ballot.
• Provide a trustworthy audit trail for each election.
• Meet WCAG 2.2 AA accessibility for the voter-facing ballot.

Architectural decisions

• Monorepo tooling: Turborepo (apps/web for marketing, apps/elections for the voting app, packages/design-system for shared CSS tokens).
• Backend: Convex (reactive DB, serverless functions, scheduled jobs, built-in auth helpers).
• Voter authentication: Emailed unique voting tokens. Admin uploads voter roll; each voter receives a one-time magic link. Ballot anonymized on submission.
• Tabulation: Both IRV and STV implemented as configurable race types.

Scope (child issues)

Foundation

• #1934 — chore(repo): migrate to Turborepo monorepo
• #1935 — feat(elections): scaffold elections app + Convex backend
• #1936 — build(elections): deploy elections.us-rse.org (DNS, hosting, CI/CD)

Data & admin

• #1937 — feat(elections): Convex schema for elections, races, candidates, voters, ballots
• #1938 — feat(elections): admin UI for election and race configuration
• #1939 — feat(elections): admin voter roll CSV import and token generation
• #1940 — feat(elections): transactional email delivery for voting tokens

Voting experience

• #1941 — feat(elections): accessible ranked-choice ballot UI
• #1942 — feat(elections): token-gated voting route with one-time-use and ballot secrecy

Tabulation & results

• #1943 — feat(elections): IRV tabulation engine with test fixtures
• #1944 — feat(elections): STV tabulation engine with test fixtures
• #1945 — feat(elections): results UI with round-by-round visualization

Trust & ops

• #1946 — feat(elections): audit log and election lifecycle state machine

Suggested sequencing

1. Foundation: #1934 → #1935 → #1936
2. Data: #1937 → #1938 → #1939 → #1940
3. Voting: #1941 in parallel with #1942
4. Tabulation: #1943 → #1944 → #1945
5. Trust: #1946 (can start once #1937 and #1938 land; finalize after #1940)

Out of scope (for now)

• Multi-org/tenant support (only US-RSE elections).
• Live streaming / real-time result broadcasting during open voting.
• Voter identity verification beyond token possession.
• Importing historical ElectionBuddy results.

Non-negotiables

• Ballot secrecy is preserved end-to-end — no admin query can map a submitted ballot back to a voter identity.
• One-person-one-ballot is enforced at the token layer.
• Every state change on an election (config, open, close, publish) is recorded in an audit log.