Colour effort by zone, and read distance in the rider's units

A watt is a fact; a zone is what it costs you. The biggest number on the
ride screen was the same shade of white at 90 W and at 400 W, which is a
thing no training app has done in fifteen years.

Zones, with two rules:

- **No reference, no zone.** An unset FTP draws the plain number. A zone
  measured against a guessed threshold would paint every ride with a
  confident lie.
- **Colour never carries it alone.** "Z4" renders beside the swatch, so
  the meaning survives a colour-blind rider, a phone in direct sun and a
  black-and-white screenshot.

Read off the rolling average, not the instantaneous watts: at 4 Hz the
raw figure crosses two boundaries every pedal stroke, and a colour that
strobes is worse than no colour. Not pedalling is not zone 1.

Units are a display preference applied at the last step before the
glass. Everything computed, stored and recorded stays SI, so a FIT file
never depends on what the screen was set to. `format.ts` takes the unit
system as an argument rather than reading a module-level setting — pure
functions are what let every readout redraw the moment it changes. The
`km` helper is gone rather than left beside `dist`, so there is no
second way to format a distance that ignores the preference.

Rust's block labels lose their baked-in kilometres. The block already
carries start_x and end_x and the frontend renders that span in the
rider's units; a kilometre in the text sat inside a sentence saying
miles everywhere else.

Also on the ride screen:

- The gradient gets a wedge beside the number. A signed decimal has to
  be read; a slope is seen. Exaggerated and clamped, because a true-scale
  6% is indistinguishable from 3% at 40 px wide.
- What is coming, from the profile's own block list — "2.1 km at 12% in
  460 m". The chart says where the rider is; what is about to happen is
  what decides whether to shift now. The data was already computed
  Rust-side and thrown away here. Close in, the small unit reads better
  than a fraction of the big one.
- Mode and target merge into one chip. They are a single fact, and
  splitting them spent a chip of header width repeating the word
  "target".
- The pod chip no longer reports a missing `+` pod while the `−` pod is
  connected. The `−` pod relays its twin, so that is the intended
  configuration — the ride screen was calling it a fault, contradicting
  the device screen two keystrokes away.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/src/components/ProfileDrawer.svelte

@@ -10,7 +10,7 @@
   import { open } from '@tauri-apps/plugin-dialog';
   import { app } from '../lib/app.svelte';
   import { api } from '../lib/bridge';
-  import { axisValue } from '../lib/format';
+  import { axisValue, dist, distUnit, elev, elevUnit } from '../lib/format';
   import type { ProfileView } from '../lib/types';
 
   let yaml = $state('');
@@ -136,9 +136,11 @@
           <span class="label">Loaded</span>
           <strong>{loaded.name}</strong>
           <span class="sample-sub">
-            {loaded.totalMetres ? `${(loaded.totalMetres / 1000).toFixed(1)} km` : ''}
+            {loaded.totalMetres ? `${dist(loaded.totalMetres, app.units, 1)} ${distUnit(app.units)}` : ''}
             {loaded.totalSeconds ? `${Math.round(loaded.totalSeconds / 60)} min` : ''}
-            {loaded.totalAscentM != null ? `· ${loaded.totalAscentM.toFixed(0)} m up` : ''}
+            {loaded.totalAscentM != null
+              ? `· ${elev(loaded.totalAscentM, app.units)} ${elevUnit(app.units)} up`
+              : ''}
             {loaded.looping ? '· loops' : ''}
           </span>
           <button class="btn ghost danger" onclick={() => app.run(() => api.clearProfile())}>
@@ -174,7 +176,7 @@
                 <em>{b.kind}</em>
                 {b.label}
                 <span class="quiet">
-                  {axisValue(b.unit, b.endX - b.startX)}
+                  {axisValue(b.unit, b.endX - b.startX, app.units)}
                 </span>
               </span>
             {/each}