Wind aloft → true heading, ground speed, ETE & fuel per leg

[msupino]

Summary

Add per-leg (or global) wind aloft input and use it to compute the wind-correction angle (WCA), true heading, ground speed, and accurate time/fuel per leg. Today the drift lines (Show drift lines) are a static 10° cosmetic reference and the Flight Plan time/fuel assume zero wind.

Motivation

Wind is the single biggest factor in real VFR planning. Without it, ETE and fuel are optimistic and headings are wrong. This is the highest-value gap.

Proposed UI

• Wind input in the Flight Plan modal: a global wind (dir°/kt) row, plus optional per-leg override cells.
• New/derived columns: WCA, TH (true heading), MH (magnetic, via existing mag var), GS (ground speed). Time and Fuel recompute from GS instead of TAS.
• Drift lines could optionally reflect the real WCA instead of a fixed angle.

Data / math

• Standard wind triangle: WCA = asin(windSpeed * sin(windDir - course) / TAS), GS = TAS*cos(WCA) + windSpeed*cos(...).
• TAS source = leg flightSpeed (currently treated as GS). Decide: treat existing speed as TAS.

Implementation

• docs/app/io.js — Flight Plan table build + CSV; add wind state to route/leg model and navaid.route schema (leg.wind or global).
• docs/app/core.js — heading/GS helpers; strings (en + he).
• docs/app/draw.js — optional: drift line angle from WCA.
• Persist global wind in localStorage / route JSON.

Acceptance criteria

• Entering wind changes GS, time, fuel, and heading columns live.
• Zero wind reproduces today's numbers.
• Wind persists in route JSON export/import.
• CSV includes the new columns.
• en + he strings.