Fix asset matching in task type CSV import

[NicoPennec]

Problem

• During task type estimations CSV import, the asset lookup key was built from literal text instead of the asset-type slug, so no asset row ever matched (regression from the %-to-f-string conversion in bf7d4fe).

Solution

• Rebuild the asset key by interpolating the asset-type slug and the asset name, restoring the original matching behavior.
• Report the raw CSV Parent/Entity values in the "not found" error instead of the internal slugified key, so the user can fix their file.