fix(database): correct metrics and improve error handling

- Fix metrics double-counting: track deltas for WaitCount/WaitDuration
  instead of adding cumulative values each tick
- Replace fmt.Printf with structured logging in pool monitor
- Add PoolOptions validation (MaxConns > 0, MinConns >= 0)
- Warn when DATABASE_URI overrides non-default PoolOptions
- Improve findAndParseConfig to report all tried files and errors
- Remove dead code in pgdb/config.go (unreachable host default)
- Fix errcheck lint issues for file.Close() calls
- Add context parameter to OpenDBMonitor() (breaking change)

database/integration_test.go

@@ -7,9 +7,7 @@ import (
 )
 
 // Mock types for testing SQLC integration patterns
-type mockQueries struct {
-	db DBTX
-}
+type mockQueries struct{}
 
 type mockQueriesTx struct {
 	*mockQueries
@@ -58,7 +56,7 @@ func TestSQLCIntegration(t *testing.T) {
 
 		// Verify our DB interface is compatible with what SQLC expects
 		var dbInterface DB[*mockQueriesTx]
-		var mockDB *mockQueries = &mockQueries{}
+		mockDB := &mockQueries{}
 		dbInterface = mockDB
 
 		// Test that our transaction helper can work with this pattern