The "what this file cannot keep" intro promises a loss on export even when every listed kind is kept #230

Found by the Dev while building #229 (#227), confirmed by the PO on a production build of 4088021.

What happens

Open a file whose only listed item is error values (or only unknown functions). The report's intro reads:

"errs.xlsx" มี 1 อย่างที่เรารู้ว่าแอปยังเก็บไว้ไม่ได้ ในแอปสิ่งเหล่านี้จะใช้ไม่ได้ และถ้าส่งออกแล้วบันทึกทับไฟล์เดิม บางอย่างจะไม่ถูกเก็บไว้

(EN: "…if you export and save over the original, it may not be kept")

But both of those kinds survive export: error values are written back as t="e" (#229), and an unknown function's formula goes out as it was. The detail line under the item says so, so the report contradicts itself.

Not a wrong number and nothing is lost, hence sev:low.

Done when

• The intro only says something will not be kept when at least one listed kind is actually lost on export (pictures, charts, shapes, pivots, names, macros, external links' cached link targets as applicable — check each against the exporter rather than this list).
• When everything listed is kept on export, the intro says what is true: it works differently in the app, the exported file keeps it.
• Both languages, singular and plural.
• A test for each branch; the existing flow for บอกผู้ใช้ตอนเปิดไฟล์ ว่าไฟล์นี้มีอะไรที่แอปเก็บไว้ไม่ได้ · Tell the user, on open, what in this file will not survive a save #83 still passes.