Backend:
- GET /api/market/prices/{ticker} now returns { bars, range_90d }
with 90-day low/high computed from market_snapshots
- POST /api/market/backfill/{ticker} fetches 90 days of daily bars
from Polygon and inserts missing bars into market_snapshots
- POST /api/market/backfill-all does the same for all active tickers
Frontend:
- Right Y-axis domain scaled to 90-day min/max (with 3% padding)
- Green dashed reference line at 90-day high
- Red dashed reference line at 90-day low
- Labels show exact price on each reference line
- Default limit bumped to 200 bars