merge: Integrate PR #229 UT infrastructure with fallback logic

## Changes
- ✅ Merge dev branch's UT infrastructure (Issue #227 fix)
- ✅ Preserve fallback mechanism for ai_model_id and exchange_id
- ✅ Use `allModels` instead of `enabledModels` (allow editing disabled model traders)
- ✅ Use `allExchanges` instead of `enabledExchanges`

## Conflict Resolution
- Combined feature/partial-close-dynamic-tpsl's defensive programming
- Adopted dev branch's core fix: allModels/allExchanges validation
- Updated error messages to reflect "not exist" vs "not enabled"

Related: #229, #227

config/database_test.go

@@ -0,0 +1,9 @@
+package config
+
+import "testing"
+
+func TestExample(t *testing.T) {
+	if 1+1 != 2 {
+		t.Error("Math is broken")
+	}
+}