Add BTC candlestick chart with local OHLC storage

- Store daily BTC OHLC candles in SQLite to avoid hitting CoinGecko on every load
- Seed with 30 days of daily candles on first boot (free tier gives daily granularity for days<=30)
- Auto-detect and replace coarse legacy candle data on startup
- Daily refresh adds new candles on each container restart
- New GET /candles endpoint (supports ?days=365 and ?days=all)
- Switch BTCHistoryChart to BTCCandlestickChart using lightweight-charts (TradingView)
- Purchase markers with nearest-candle matching and multi-purchase merging
- Fullscreen mode showing all stored candles
- Fix frontend port to 3001 and pass REACT_APP_API_URL as build arg

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

btc-portfolio/backend/app/services/btc.py

@@ -1,4 +1,5 @@
 import requests
+from datetime import datetime, timezone
 
 
 def get_btc_history_eur() -> list:
@@ -14,6 +15,40 @@ def get_btc_history_eur() -> list:
         return []
 
 
+def get_btc_ohlc_eur(days: int) -> list:
+    """Fetch OHLC candles from CoinGecko. Returns [[ts_ms, open, high, low, close], ...]."""
+    try:
+        resp = requests.get(
+            "https://api.coingecko.com/api/v3/coins/bitcoin/ohlc",
+            params={"vs_currency": "eur", "days": str(days)},
+            timeout=20,
+        )
+        resp.raise_for_status()
+        return resp.json()  # [[timestamp_ms, open, high, low, close], ...]
+    except Exception:
+        return []
+
+
+def aggregate_to_daily(raw: list) -> dict:
+    """Collapse intraday OHLC rows into one candle per UTC calendar date.
+
+    Returns {date_str: {open, high, low, close}} using first open, max high,
+    min low, last close per day.
+    """
+    by_date: dict = {}
+    for row in raw:
+        ts_ms, o, h, l, c = row
+        date = datetime.fromtimestamp(ts_ms / 1000, tz=timezone.utc).strftime("%Y-%m-%d")
+        if date not in by_date:
+            by_date[date] = {"open": o, "high": h, "low": l, "close": c}
+        else:
+            existing = by_date[date]
+            existing["high"] = max(existing["high"], h)
+            existing["low"] = min(existing["low"], l)
+            existing["close"] = c  # last close wins
+    return by_date
+
+
 def get_btc_price_eur() -> float:
     try:
         resp = requests.get(

btc-portfolio/backend/app/services/candles.py

@@ -0,0 +1,73 @@
+import logging
+from datetime import datetime, timezone, date as dt_date
+
+from sqlalchemy.orm import Session
+
+from ..models import OHLCCandle
+from .btc import get_btc_ohlc_eur, aggregate_to_daily
+
+logger = logging.getLogger(__name__)
+
+
+def seed_candles(db: Session) -> None:
+    """Fetch 30 days of daily OHLC candles from CoinGecko and store them.
+    Free tier gives 4-hour bars for days<=30, which aggregate cleanly to daily candles.
+    days>30 drops to 4-day granularity (unusable for a daily chart).
+    """
+    raw = get_btc_ohlc_eur(days=30)
+    if not raw:
+        logger.warning("Candle seed: CoinGecko returned no data — will retry on next startup.")
+        return
+
+    daily = aggregate_to_daily(raw)
+    rows = [
+        OHLCCandle(date=date, open=v["open"], high=v["high"], low=v["low"], close=v["close"])
+        for date, v in sorted(daily.items())
+    ]
+    for row in rows:
+        db.merge(row)
+    db.commit()
+    logger.info("Candle seed: stored %d daily candles (%s → %s).", len(rows), min(daily.keys()), max(daily.keys()))
+
+
+def refresh_latest_candles(db: Session) -> None:
+    """Add any missing candles up to today. Seeds the DB if empty.
+    Also detects and replaces coarse (>2-day gap) legacy data from a previous days=365 seed.
+    """
+    # Sparse-data detection: if existing candles have >2-day gaps, wipe and re-seed
+    first_two = db.query(OHLCCandle).order_by(OHLCCandle.date.asc()).limit(2).all()
+    if len(first_two) == 2:
+        d1 = dt_date.fromisoformat(first_two[0].date)
+        d2 = dt_date.fromisoformat(first_two[1].date)
+        if (d2 - d1).days > 2:
+            logger.warning("Candle refresh: detected coarse candle data (gap=%d days). Wiping and re-seeding with daily candles.", (d2 - d1).days)
+            db.query(OHLCCandle).delete()
+            db.commit()
+            seed_candles(db)
+            return
+
+    latest = db.query(OHLCCandle).order_by(OHLCCandle.date.desc()).first()
+
+    if latest is None:
+        seed_candles(db)
+        return
+
+    today = datetime.now(tz=timezone.utc).strftime("%Y-%m-%d")
+    if latest.date >= today:
+        return  # Already up to date
+
+    raw = get_btc_ohlc_eur(days=7)
+    if not raw:
+        logger.warning("Candle refresh: CoinGecko returned no data.")
+        return
+
+    daily = aggregate_to_daily(raw)
+    new_dates = [d for d in daily if d > latest.date]
+    if not new_dates:
+        return
+
+    for date in new_dates:
+        v = daily[date]
+        db.merge(OHLCCandle(date=date, open=v["open"], high=v["high"], low=v["low"], close=v["close"]))
+    db.commit()
+    logger.info("Candle refresh: upserted %d candle(s) up to %s.", len(new_dates), max(new_dates))