fix(geometry): check height overflow when white-space is nowrap

[LeadcodeDev]

Severity Low, category correctness. Location: crates/rustmotion/src/cli/commands/geometry.rs:844

Impact

check_unwrappable_text — the only check left for a nowrap node — compares width only and always emits Axis::X (geometry.rs:781-793). So the Y axis is unchecked for any white-space: nowrap|pre text. {"type":"text","content":"Hi","style":{"font-size":"120px","white-space":"nowrap","height":"40px"}} has a single line ~156px tall painted out of a 40px content box and validates clean; delete the white-space key and the identical fixture is correctly reported as ContentOverflowsBox/Axis::Y (proved by the existing test wrapped_text_taller_than_its_fixed_height_card_is_flagged, geometry.rs:2806). The stated rationale only justifies skipping the wrap-dependent width re-measure; a nowrap node's height is exactly one line_height and needs no wrapping to compute.

Fix

Instead of returning early on nowrap, measure with (AvailableSpace::MaxContent, AvailableSpace::Definite(ch)) and report only the Y axis (leave X to check_unwrappable_text), so a single unwrapped line taller than its box is still caught.

Evidence the audit read

// nowrap/pre is check_unwrappable_text's territory: re-measuring it
// here at a constrained width would wrap text that will actually
// paint as one (too-wide) line, producing a height number that
// doesn't correspond to anything that gets painted.
if nowrap {
    return;
}

Stacked on fix/geometry-text-overflow-box, which carries the previous finding of this workstream. GitHub shows only this finding's diff; merge in order.

Part of the September 2026 audit remediation chantier. Refs #220 (RM-32).