test: Add minimal UT infrastructure and fix Issue #227

This commit sets up a minimal, KISS-principle testing infrastructure
for both backend and frontend, and includes the fix for Issue #227.

Backend Changes:
- Add Makefile with test commands (test, test-backend, test-frontend, test-coverage)
- Add example test: config/database_test.go
- Fix Go 1.25 printf format string warnings in trader/auto_trader.go
  (Changed log.Printf to log.Print for non-format strings)
- All backend tests pass ✓

Frontend Changes:
- Add Vitest configuration: web/vitest.config.ts (minimal setup)
- Add test utilities: web/src/test/test-utils.tsx
- Add example test: web/src/App.test.tsx
- Add dependencies: vitest, jsdom, @testing-library/react
- All frontend tests pass ✓

Issue #227 Fix:
- Fix AITradersPage to allow editing traders with disabled models/exchanges
- Change validation to use allModels/allExchanges instead of enabledModels/enabledExchanges
- Add comprehensive tests in web/src/components/AITradersPage.test.tsx
- Fixes: https://github.com/tinkle-community/nofx/issues/227

CI/CD:
- Add GitHub Actions workflow: .github/workflows/test.yml
- Non-blocking tests (continue-on-error: true)
- Runs on push/PR to main and dev branches

Test Results:
- Backend: 1 test passing
- Frontend: 5 tests passing (including 4 for Issue #227)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: tinkle-community <tinklefund@gmail.com>

web/src/components/AITradersPage.tsx

@@ -165,8 +165,8 @@ export function AITradersPage({ onTraderSelect }: AITradersPageProps) {
     if (!editingTrader) return;
 
     try {
-      const model = enabledModels?.find(m => m.id === data.ai_model_id);
-      const exchange = enabledExchanges?.find(e => e.id === data.exchange_id);
+      const model = allModels?.find(m => m.id === data.ai_model_id);
+      const exchange = allExchanges?.find(e => e.id === data.exchange_id);
 
       if (!model) {
         alert(t('modelConfigNotExist', language));
@@ -764,8 +764,8 @@ export function AITradersPage({ onTraderSelect }: AITradersPageProps) {
           isOpen={showEditModal}
           isEditMode={true}
           traderData={editingTrader}
-          availableModels={enabledModels}
-          availableExchanges={enabledExchanges}
+          availableModels={allModels}
+          availableExchanges={allExchanges}
           onSave={handleSaveEditTrader}
           onClose={() => {
             setShowEditModal(false);