test(competitions): unit tests for loader, filters and date flattening

[AnayDhawan]

Blocked by #195 and #201.

Unit tests for the pure logic in the competitions vertical. The repo has 16 test files and 129 tests; this vertical should not be the part with none.

Setup that already exists

Vitest 4.1.9 with jsdom, @testing-library/react. vitest.config.ts includes src/**/*.test.ts and src/**/*.test.tsx, so tests are colocated next to what they test. npm run test:unit. CI runs it on every PR via the unit-tests job in .github/workflows/ci.yml.

Closest models: src/lib/places.test.ts for the filtering shape, src/lib/data-freshness.test.ts for date logic, src/components/map/results-list.test.tsx for a component test.

What to cover

src/lib/competitions.test.ts

• filterCompetitions with each filter alone, and with two composed
• Age filter is inclusive at both ends of age_min and age_max
• query matches name, organizer and subjects, case-insensitively, and ignores surrounding whitespace
• Empty filters returns everything; a filter matching nothing returns an empty array, not undefined
• nextDate skips past dates, returns the soonest future one, and returns undefined when all dates are past
• upcomingDates sorts ascending and includes country stages only when a country is given

src/lib/competition-events.test.ts

• Flattening produces one event per date plus one per stage of the selected country only
• A competition with no country_tracks produces only its own dates
• The estimated flag survives flattening
• Timezone handling does not shift a date across a day boundary. Pin a fixed now rather than using the real clock.

Date tests must not depend on when they run. check-data-freshness.mjs already accepts a --today= flag for exactly this reason. Pass an explicit now everywhere rather than letting a test pass in September and fail in January.

Acceptance criteria

• npm run test:unit passes
• No test depends on the current date
• Filter composition is covered, not just single filters
• Country-stage flattening is covered
• Tests colocated in src/lib/, matching the existing convention