fix(api): aggregate metrics history by day so days=42 spans days, not minutes

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bot/data/db.py

@@ -330,9 +330,21 @@ class Database:
             return result
 
     async def get_metrics_history(self, days: int = 42) -> list[dict]:
+        """Return the closing snapshot of each UTC day, newest day first.
+
+        metrics_daily receives one snapshot per trading cycle (~1/min), so a
+        plain LIMIT over raw rows would cover minutes, not days. DISTINCT ON
+        collapses each calendar day to its last snapshot, making `days` bound
+        actual days. history[0] remains the most recent snapshot overall.
+        """
         async with self._pool.acquire() as conn:
             rows = await conn.fetch(
-                "SELECT * FROM metrics_daily ORDER BY timestamp DESC LIMIT $1", days
+                """
+                SELECT DISTINCT ON (timestamp::date) *
+                FROM metrics_daily
+                ORDER BY timestamp::date DESC, timestamp DESC
+                LIMIT $1
+                """, days
             )
             return [dict(r) for r in rows]