feat: FF→FRED series mapping + MacroSeries visualization page

Backend:
- ff_calendar: add series_id column (migration) + FF_TO_FRED mapping dict
  (NFP→PAYEMS, CPI→CPIAUCSL, Jobless Claims→ICSA, GDP→GDPC1, FEDFUNDS, PCE)
- import_csv + sync_live now populate series_id on each FF event
- New GET /api/eco/series/{id}/history: FRED time series + linked FF events
  (surprises, forecast, actual) merged by date — enables context queries

Frontend:
- New MacroSeriesPage.tsx: sidebar with 11 FRED series grouped by category,
  recharts ComposedChart with area + z-score surprise reference lines (|z|≥1.5),
  KPI cards (latest/prev/min/max), FF events table (actual vs forecast coloring),
  z-score bar chart for recent surprises, range selector (1Y/2Y/5Y/10Y/All)
- Route /macro-series + Sidebar entry "Macro Series"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/services/database.py

@@ -696,6 +696,7 @@ def init_db():
         actual_value TEXT,
         forecast_value TEXT,
         previous_value TEXT,
+        series_id TEXT,
         detail TEXT,
         source TEXT DEFAULT 'ff_cache',
         fetched_at TEXT DEFAULT (datetime('now')),
@@ -705,8 +706,14 @@ def init_db():
         c.execute("CREATE INDEX IF NOT EXISTS idx_ff_date ON ff_calendar(event_date)")
         c.execute("CREATE INDEX IF NOT EXISTS idx_ff_currency ON ff_calendar(currency)")
         c.execute("CREATE INDEX IF NOT EXISTS idx_ff_impact ON ff_calendar(impact)")
+        c.execute("CREATE INDEX IF NOT EXISTS idx_ff_series ON ff_calendar(series_id)")
     except Exception:
         pass
+    # Migration: add series_id column if missing (existing deployments)
+    try:
+        c.execute("ALTER TABLE ff_calendar ADD COLUMN series_id TEXT")
+    except Exception:
+        pass  # Column already exists
 
     # ── Specialist Desks ───────────────────────────────────────────────────────
     c.execute("""CREATE TABLE IF NOT EXISTS specialist_reports (