test: Vitest coverage infra + backfill to 85% coverage mandate

[Wikid82]

Summary

• Adds Vitest + React Testing Library, replacing the node:test runner. Server/action/lib tests run in plain Node (jose's Uint8Array checks break under jsdom's separate realm); component tests opt into jsdom per-file via a // @vitest-environment jsdom docblock.
• Adds codecov.yml + .github/workflows/codecov.yml gating project and patch coverage at 85%, mirroring the Charon setup. ci.yml's test step now runs npm run test:coverage so the 85% floor is enforced even before the Codecov GitHub App/secret are wired up on this repo.
• Adds scripts/check-patch-coverage.mjs (npm run coverage:patch) — a dependency-free Node script that diffs coverage/lcov.info against a git baseline to report patch coverage locally, plus .claude/commands/fix-patch-coverage.md (Hestia's equivalent of Charon's /fix-patch-coverage) to close gaps before pushing.
• Backfills real unit/component tests for the previously-untested action layer (chores, rewards, reminders, members, household, profile, auth), auth/session.ts, auth/current-user.ts, proxy.ts, and 16 components. Real coverage goes from ~12% to 99.4% lines / 90.6% branches / 100% functions.
• Server-logic tests run against a real in-memory SQLite DB (migrated fresh per test file) with next/headers, next/cache, and next/navigation mocked in src/test/setup.ts — redirect() throws Error("NEXT_REDIRECT:<path>"), asserted on directly rather than mocked away.
• page.tsx/layout.tsx route entrypoints, db/schema.ts, db/index.ts, and instrumentation.ts are excluded from the coverage mandate (thin composition/declarative/bootstrap code, exercised by e2e/household-flow.spec.ts instead) — same ignore list in codecov.yml, vitest.config.ts, and the patch-coverage script.

Note on workflow files: this PR includes changes to .github/workflows/ci.yml and adds .github/workflows/codecov.yml, rather than committing those straight to main per the repo's usual convention. They depend on the accompanying package.json/vitest.config.ts changes in this same PR — landing them on main first would break main's CI until this merges down through development. Flagging this explicitly since it's a deviation from the documented workflow-files-go-to-main rule.

Still needed from a maintainer (can't be done from here): install the Codecov GitHub App on this repo and add a CODECOV_TOKEN repository secret for .github/workflows/codecov.yml to actually upload — until then, the codecov job will fail at the upload step (tests/coverage/build all still pass regardless).

Test plan

• npm run test:coverage — 172 tests pass, 99.41% lines / 90.61% branches / 100% functions / 99.09% statements (threshold: 85% lines)
• npm run lint — clean
• npm run build — clean, TypeScript passes
• node scripts/check-patch-coverage.mjs — manually verified it correctly flags an uncovered synthetic change and correctly reports clean when reverted
• Install Codecov GitHub App + add CODECOV_TOKEN secret (maintainer action, see note above)

🤖 Generated with Claude Code

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