i18n: document framework ok.po msgid baseline and info_set translation contract

Per BnanZ0/ok-nte#112, missing msgids and task strings should be reported here.

When testing ok-nte with zh_TW, the task info panel still shows simplified Chinese for strings like 轮次, 开启, 任务结束. TaskTab already calls og.app.tr() on info_set keys/values (ok/gui/tasks/TaskTab.py:86-90); the issue is that derived projects' ok.po does not include these msgids.

Request

1. Framework msgid baseline — Publish a list of strings that ok-script itself looks up via og.app.tr() / info_set (e.g. Log, Warning, Error, Alert, Confirm, Cancel, Export failed, …) so derived apps know what to add to ok.po.

2. info_set translation contract — Document that derived tasks should use static simplified-Chinese msgids in info_set() (no tr() in tasks); display is handled by TaskTab. Include common key/value examples for translators.

3. (Optional) Improve gen_tr_po_files() / to_translate export so derived projects can dump a complete missing-msgid list from runtime.

Note: ok-nte#112 is kept for the MainWindow.py / app.py notification-path bug (og.app.tr vs QCoreApplication.translate). This issue covers msgid catalog and documentation only.

Start with ok/gui/tasks/TaskTab.py:86-90 and inspect the framework’s og.app.tr() and info_set usage, along with gen_tr_po_files() and to_translate. Document the framework msgid baseline and the info_set contract with translator examples; done means derived projects can identify the required ok.po entries, with the export improvement treated as optional.