Optimize site loading performance

[nedcut]

Motivation

• Reduce initial client bundle size and improve perceived load time by avoiding heavy runtime imports and warming network paths for the map.
• Prevent large utility code (Turf length) from being pulled into the main page graph while keeping identical distance and bounds behavior.
• Improve first-byte and resource fetch speed for Mapbox and static image assets with connection hints and caching hints.

Description

• Replaced the Turf length usage in lib/geo.ts with a small in-repo haversine implementation (segmentDistanceMeters and geometryDistanceMeters) used by lineDistanceMeters, coordinateBounds, and routeFeatureCollection so route/bounds math no longer imports Turf length into the page graph.
• Added preconnect and dns-prefetch link hints for Mapbox origins in app/layout.tsx to warm the network connection before the dynamic map initializes.
• Added Next.js experimental package import optimization for lucide-react and an HTTP header rule in next.config.mjs to set Cache-Control: public, max-age=31536000, immutable for static image asset paths to enable long-lived caching.
• Kept runtime behavior and API signatures unchanged so application logic and UI quality are preserved, and left a note that a full Turf split (install/uninstall) could not be performed in this environment.

Testing

• Ran npm run test (Vitest) and all unit tests passed: 23 files, 192 tests (passed).
• Ran npm run typecheck && npm run lint && npm run build and the build/typegen completed successfully while ESLint reported one pre-existing warning in lib/hooks/useMembership.ts.
• Attempting npm run test -- --runInBand failed because Vitest does not accept the Jest --runInBand flag, which is a tooling invocation mismatch rather than a code regression.

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Codex Task

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Project	Deployment	Actions	Updated (UTC)
lofoten-map	Ready	Preview, Comment	Jun 17, 2026 10:48pm

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[nedcut]

Closing as superseded. The same goals (drop Turf length from the page graph, Mapbox connection warming, caching) landed via #10 and follow-ups on main. This branch is conflicting and stale.