With a fixed font size, a text field's appearance cuts a long value at
the edge of its box, but form_fill only answered "filled": n. A person
sees the cut; an agent filling forms through the CLI or MCP did not.
The text appearance builder now notes when the text it lays out does
not fit: one line wider than the box, or wrapped lines below it.
forms::appearance::value_overflow asks that for a field's widget,
Document::field_overflow for a field by name, and form_fill adds a
warning for each filled field that is cut off. The value is still saved
whole and drawn as before; auto-sized fields shrink to fit and are not
reported.
The automation tests' inline PDF builder moves to a shared pdf_of.
Fixes#4018