fix: reduce candidate coin limit to 10, fix Select scroll and flash

- Lower MaxCandidateCoins from 50 to 10 (backend)
- Update CoinSourceEditor: options 1-10, default 3, max static coins 10
- Fix NofxSelect dropdown closing on internal scroll
- Fix NofxSelect position flash on open (useLayoutEffect)

store/strategy.go

@@ -12,7 +12,7 @@ import (
 
 // Hard limits to prevent token explosion in AI requests
 const (
-	MaxCandidateCoins = 50
+	MaxCandidateCoins = 10
 	MaxPositions      = 3
 	MaxTimeframes     = 4
 	MinKlineCount     = 10