cmd/stripes: page auto only when wrapped height exceeds terminal

[achille-roussel]

Problem

When rendering JSON/XML with --paging=auto, the pager was spawned even for tiny documents that fit on screen. The auto-pager triggered the moment any single rendered line was wider than the terminal — and JSON/XML almost always have at least one wide line (long string values, deep nesting). A 3-line document got paged just because one value was 89 cells wide on an 80-column terminal.

Fix

A wide line isn't a reason to page — the terminal wraps it. What matters is the total display rows after wrapping vs. terminal height. The auto-pager now:

• Counts each logical line as ceil(displayWidth / termWidth) screen rows (new wrappedRows helper), and
• Spawns the pager only once the running row total exceeds the terminal height.

The standalone "one wide line" trigger is gone. Streaming behavior and ANSI-aware width measurement are unchanged.

Behavior

Input	Before	After
Short doc, one wide line on 80 cols	paged ❌	not paged ✓
40-key object (~42 rows)	paged	paged ✓
One value ~2500 cells → wraps past a 24-row screen	paged (by width)	paged (by wrapped height) ✓

Tests

• TestWrappedRows — unit coverage for the arithmetic (empty line, exact-fit, boundaries, div-by-zero guard).
• Split the old TestPagingAutoWideContentPages into TestPagingAutoWideButShortNoPager (the reported case) and TestPagingAutoWideWrappingPastHeightPages (wide content that legitimately overflows via wrapping).
• PTY tests skip in sandboxed CI without a controlling terminal; verified all three cases by driving the built binary through a real PTY (script) with the stub pager.

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