Fuel reserves & endurance check (reserve, alternate, bingo)

[msupino]

Summary

Extend the fuel calculator with reserves and an endurance check: VFR reserve (configurable, default 30/45 min), optional alternate fuel, and a comparison of total required fuel vs usable tank capacity.

Motivation

Total burn alone doesn't tell a pilot if the flight is legal/safe. Reserve + tank capacity = go/no-go.

Proposed UI

• Aircraft inputs add usable fuel (gal) and reserve (min).
• Flight Plan totals show: trip fuel, reserve fuel, (alternate fuel), total required, remaining, and an endurance figure.
• Red warning when total required > usable.

Implementation

• docs/app/io.js — totals row; navaid.aircraft schema gains usableGal, reserveMin.
• docs/app/core.js — strings (en + he).

Acceptance criteria

• Reserve + capacity inputs persist in navaid.aircraft.
• Totals show required vs remaining and endurance.
• Over-tank warning.
• CSV includes the summary.
• en + he strings.