feat(tests): add comprehensive test suite, update deps and Go 1.26.1

- Add 20+ tests for utility functions, SharedData, and Model
- Tests cover: LoadTables, LoadTableData, UpdateCell, pagination,
  table inference, focus/blur, empty database, invalid indices
- Update Go to 1.26.1, upgrade all dependencies
- Replace custom Min/Max with Go builtin min/max
- Format all files with goimports
- Add staticcheck to CI workflow

internal/app/app.go

@@ -522,20 +522,6 @@ func WrapText(text string, width int) []string {
 	return lines
 }
 
-func Min(a, b int) int {
-	if a < b {
-		return a
-	}
-	return b
-}
-
-func Max(a, b int) int {
-	if a > b {
-		return a
-	}
-	return b
-}
-
 func InitialModel(db *sql.DB, opts ...Option) *Model {
 	shared := NewSharedData(db)
 	if err := shared.LoadTables(); err != nil {