whatif: live data refresh, inflation-adjusted spending, legend fix

Three follow-ups to the actualbudget integration:

**Always-fresh autofill.** Drop the one-shot `*AutoFilled` boolean
gates; replace with `nwUserEdited` / `spendingUserEdited` flags. Until
the user types into either field, every refetch (mount, window
focus) updates the form value. Once they edit, we leave it alone. A
small ↻ button next to each anchor input flips the edited flag back
off so the user can re-snap to live data on demand. React Query
configured with staleTime=0 + refetchOnMount='always' +
refetchOnWindowFocus=true so the cache never serves stale numbers.
NW provenance shows the snapshot date.

**Inflation-adjusted spending.** Backend now revalues each trailing
month's nominal pence forward to today's £ using monthly compounding
of `inflation_pct` (default 0.03 ≈ UK CPI 2024-26). Headline
`total_gbp` is the real-£ figure — matches the simulator's
real-GBP convention. Response also includes `nominal_total_gbp` and
`inflation_pct` for transparency. New /spending/annual?inflation_pct=
override param. 10/10 actualbudget tests pass.

**FanChart legend.** The bottom-anchored legend was overlapping the
x-axis label. Moved to top: 8 with itemGap=18 + type=scroll for
narrow viewports; bumped grid top→48 / bottom→56 + xAxis nameGap→28
so nothing collides.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/components/FanChart.tsx

@@ -135,7 +135,9 @@ function buildFan(yearly: ProjectionPoint[], showWithdrawal: boolean): EChartsOp
   }
 
   return {
-    grid: { left: 60, right: showWithdrawal ? 70 : 24, top: 30, bottom: 40 },
+    // Grid: leave room above for the legend (top:48) and below for the
+    // x-axis name label so neither collides with the chart area.
+    grid: { left: 60, right: showWithdrawal ? 70 : 24, top: 48, bottom: 56 },
     tooltip: {
       trigger: 'axis',
       formatter: (params) => {
@@ -157,7 +159,16 @@ function buildFan(yearly: ProjectionPoint[], showWithdrawal: boolean): EChartsOp
       },
     },
     legend: {
-      bottom: 0,
+      // Above the chart, centred — out of the way of the x-axis label.
+      // `type: 'scroll'` lets ECharts paginate items on narrow viewports
+      // instead of wrapping them into the chart area.
+      top: 8,
+      left: 'center',
+      type: 'scroll',
+      itemGap: 18,
+      itemWidth: 14,
+      itemHeight: 10,
+      textStyle: { fontSize: 11, color: '#475569' },
       data: [
         'median',
         'p10',
@@ -171,7 +182,8 @@ function buildFan(yearly: ProjectionPoint[], showWithdrawal: boolean): EChartsOp
       data: years,
       name: 'years from now',
       nameLocation: 'middle',
-      nameGap: 24,
+      nameGap: 28,
+      nameTextStyle: { color: '#64748b' },
     },
     yAxis: [
       {