Show the saving in the listing capsule on its own line

Station and Favourite rows share one capsule, so both now read
"Save / £3.10" and "Costs / £1.20 more" instead of the amount-free
"Saves" / "Costs more". "(approx.)" is appended on its own line when the
journey behind the figure was estimated. Break even carries no figure —
±£0.05 is noise — so it stays a single line unless the qualifier adds one.

- Split `listingCapsuleHeadline()` into a structured `ListingVerdict`
  (headline / amount / qualifier) drawn as one Text per line, so where the
  capsule breaks is decided by the data rather than by the width the price
  column happened to hand it: the figure can never straddle two lines.
- The capsule's shape follows its line count: one line stays a Capsule, two
  or more switch to a rounded rect at 8pt, whose corners do not crowd a
  taller block the way a pill's semicircular ends do.
- The Key sheet's legend renders the same component with `showsAmount:
  false`, so it demonstrates the wording without displaying the placeholder
  £1.00 figure it was built from.
- The new words ("Save", "Costs", "(approx.)", "%@ more") go into
  Localizable.strings so the copy editor owns them; amounts run through
  FuelSavingsFormat.money and the amount line is monospaced.
- VoiceOver keeps the single-line form, since a drawn break is a pause
  mid-phrase when spoken.

Tests cover the line structure for all four statuses, the estimated
qualifier and the amount-free legend. Pixel measurement on the simulator
confirms the shape rule: one line measures a radius of h/2 (a pill), two
lines measure 8pt, in both light and dark.

FuelBoard/StationsView.swift

@@ -465,7 +465,9 @@ private struct KeySavingsCapsule: View {
     }
 
     var body: some View {
-        ListingFuelSavingsCapsule(result: result)
+        // The legend demonstrates the wording, not a figure: `result` above is a
+        // placeholder verdict, and its £1.00 must never reach the screen.
+        ListingFuelSavingsCapsule(result: result, showsAmount: false)
     }
 }