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/table_list_keys.go

@@ -87,4 +87,4 @@ func (k TableListKeyMap) FullHelp() [][]key.Binding {
 		{k.Enter, k.Search, k.Escape, k.Refresh},
 		{k.GoToStart, k.GoToEnd, k.SQLMode, k.ToggleHelp},
 	}
-}
+}