Retire the Best Value proximity alert option; move Key sheet copy into a tested model

- Alerts: drop the alert-type picker and the Best Value alert path, so
  proximity alerts always follow the cheapest station. A stored `bestValue`
  selection now falls back to cheapest when loaded.
- Key sheet: the price-rating, savings, station-label and favourite wording
  comes from `KeySheetContent` in Shared/FuelSavings.swift — a Foundation-only
  model with tests that pin the exact meaning of each indicator — and the
  sheet is built from that model rather than inline strings.
- BACKLOG: record the plan to restore Best Value proximity alerts behind one
  shared evaluator (user-location baseline, a single disclosed qualification
  rule, and real/Test alert parity).
- Bump CURRENT_PROJECT_VERSION to 29.

BACKLOG.md

@@ -106,6 +106,24 @@ Status: TODO / IN PROGRESS / DONE / BLOCKED.
   scene (CPListTemplate) for navigation deep-links.
 - [ ] **Alert region tuning** — make alert trigger radius + dedup window
   user-configurable (currently fixed 300 m trigger / 1 per station per hour).
+- [ ] **Restore Best Value proximity alerts after fixing evaluation parity** —
+  the option is intentionally removed from the Alerts tab and legacy selections
+  fall back to `Cheapest station` until this is implemented. Root cause: the live
+  geofence path calculates journeys from the entered station, making that station
+  its own zero-saving baseline and therefore unable to clear any positive minimum
+  saving, while Test alert calculates from the user's location and can pass.
+  Future implementation must obtain a fresh user fix on region entry; fetch,
+  radius-filter, choose the closest eligible baseline and calculate every journey
+  from that user location; then notify only when the entered station is the best
+  qualifying candidate. Real and Test alerts must call one shared pure evaluator.
+  Apply one disclosed qualification rule everywhere (real alert, Test alert and
+  BEST VALUE badge): remove the live path's hidden extra £0.50 estimate margin,
+  compare the same penny-rounded amount shown to the user while retaining raw
+  precision for ranking, and pass the current threshold explicitly into station
+  rows instead of reading persistence per row. Regression coverage: entered
+  station can qualify, a better nearby candidate blocks it, real/Test parity,
+  exact and display-rounding boundaries, estimated/confirmed parity, immediate
+  threshold changes, and below-threshold rejection.
 - [ ] **Price-drop alerts: threshold control + Check now** — keep the current
   cache-first / 12 h refresh policy, but add a per-alert sensitivity control
   for favourite price-drop alerts instead of a fetch-frequency slider. Scope: