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>

fire_planner/actualbudget.py

@@ -127,25 +127,49 @@ def _today() -> date:
     return date.today()
 
 
+def _months_between(older: str, newer: str) -> int:
+    """Calendar months from `older` to `newer` (both YYYY-MM)."""
+    yo, mo = (int(p) for p in older.split("-"))
+    yn, mn = (int(p) for p in newer.split("-"))
+    return (yn - yo) * 12 + (mn - mo)
+
+
+def _inflation_factor(months_age: int, annual_inflation_pct: float) -> float:
+    """Multiplier to convert nominal £ at a point `months_age` months
+    in the past into today's real £. Compounds monthly so the curve
+    is smooth, not stair-stepped."""
+    if months_age <= 0:
+        return 1.0
+    monthly = (1.0 + annual_inflation_pct) ** (1.0 / 12.0)
+    return float(monthly ** months_age)
+
+
 async def fetch_trailing_spending(
     months: int,
     exclude_groups: frozenset[str],
+    annual_inflation_pct: float = 0.03,
     client_factory: ActualBudgetClient | None = None,
     today: date | None = None,
-) -> tuple[list[MonthSpend], Decimal]:
-    """Fetch trailing-N-months spending and return (per-month breakdown,
-    total in £).
+) -> tuple[list[MonthSpend], Decimal, Decimal]:
+    """Fetch trailing-N-months spending and return (per-month
+    breakdown, nominal-£ total, today's-£ inflation-adjusted total).
 
     `exclude_groups` is a set of category-group names whose spending
     should NOT count towards the consumption total — typical example
     is "Investments and Savings", which is a wealth transfer rather
     than consumption.
 
-    Months are fetched concurrently. Missing months (e.g. user joined
-    actualbudget mid-year) come back with empty `by_group`.
+    Months older than the current one are revalued to today's £ using
+    `annual_inflation_pct` compounded monthly. The fire-planner
+    simulator works entirely in REAL GBP, so the real-£ total is the
+    one to feed back as the "Annual spending" default.
+
+    Missing months (e.g. user joined actualbudget mid-year) come back
+    with empty `by_group`.
     """
     cli = client_factory or ActualBudgetClient()
-    target_months = _trailing_months(today or _today(), months)
+    today_d = today or _today()
+    target_months = _trailing_months(today_d, months)
     available_set = None  # only fetch if the API surfaces fewer months than asked
 
     async with httpx.AsyncClient() as http:
@@ -159,8 +183,18 @@ async def fetch_trailing_spending(
         for m in kept:
             spends.append(await cli.fetch_month(http, m))
 
-    total_pence = sum(
-        amt for ms in spends for name, amt in ms.by_group.items() if name not in exclude_groups
-    )
-    total_gbp = (Decimal(total_pence) / Decimal(100)).quantize(Decimal("0.01"))
-    return spends, total_gbp
+    today_month = f"{today_d.year:04d}-{today_d.month:02d}"
+    nominal_pence = 0
+    real_pence_float = 0.0
+    for ms in spends:
+        age = _months_between(ms.month, today_month)
+        factor = _inflation_factor(age, annual_inflation_pct)
+        for name, amt in ms.by_group.items():
+            if name in exclude_groups:
+                continue
+            nominal_pence += amt
+            real_pence_float += amt * factor
+
+    nominal_gbp = (Decimal(nominal_pence) / Decimal(100)).quantize(Decimal("0.01"))
+    real_gbp = (Decimal(str(round(real_pence_float / 100, 2)))).quantize(Decimal("0.01"))
+    return spends, nominal_gbp, real_gbp