Refactor barogram-map synchronization

[JEK58]

Summary

• replace the Chart.js tooltip callback event bus with a requestAnimationFrame-coalesced timestamp cursor
• synchronize map markers by nearest timestamp across independently sampled main and Airbuddy tracks
• update Leaflet layers imperatively and diff Airbuddy layers without recreating the main track or static markers
• simplify replay, decimate chart rendering, cache METAR selection, and remove obsolete synchronization composables

Why

The previous tooltip-driven synchronization performed Chart.js hit-testing, tooltip callbacks, and deep Vue/Leaflet updates for each pointer event. This refactor keeps chart pointer handling outside Chart.js and only moves changed markers.

Validation

• pnpm typecheck
• focused ESLint
• pnpm exec cypress run --spec cypress/e2e/helpers/flightCursorHelpers.cy.js
• pnpm build
• live frontend check against flight 86625 through a local live-API proxy