Virtual gearing, trainer-speed blend, and cadence decode

Gears are expressed as an offset to the commanded gradient, leaving the
physics on the route's true gradient so shifting changes effort, not speed.
Neutral gear commands exactly the route gradient, so an un-shifted ride is
unchanged.

Cadence is not in FTMS on this trainer but is on its Zwift channel, decoded
against captured frames. The undeclared FTMS trailing bytes were ruled out:
wheel RPM restated at a fixed 73.8x speed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

run.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Launch BikeControl. Always builds first via `cargo tauri build`, because a
+# plain `cargo build` produces a binary wired to localhost:1420 that shows a
+# BLACK WINDOW unless a Vite dev server happens to be running. Incremental
+# builds take seconds, and this removes a whole class of confusion.
+set -e
+ROOT="$(cd "$(dirname "$0")" && pwd)"
+LOG="$ROOT/bikecontrol.log"
+
+# WebKitGTK 2.52 on Wayland + Intel paints black rectangles via its DMABUF
+# renderer; disabling it costs nothing here (the UI is 2D canvas and CSS).
+export WEBKIT_DISABLE_DMABUF_RENDERER=1
+export WEBKIT_DISABLE_COMPOSITING_MODE=1
+export RUST_LOG="${RUST_LOG:-debug,btleplug=info,tao=warn,wry=warn}"
+
+echo "building (embeds the frontend — this is what avoids the black window)..."
+( cd "$ROOT/src-tauri" && cargo tauri build --debug --no-bundle ) 2>&1 | tail -3
+
+BIN="$ROOT/target/debug/bikecontrol-app"
+echo "=== BikeControl $(date '+%H:%M:%S') ===" > "$LOG"
+echo "launching $BIN — logging to $LOG"
+exec "$BIN" "$@" 2>&1 | tee -a "$LOG"