fix(geometry): compare terminal height in a single box model

[LeadcodeDev]

Severity Low, category correctness. Location: crates/rustmotion/src/cli/commands/geometry.rs:963

Impact

bbox.h is layout.height, the border box. LegacyPaintDispatcher::dispatch treats only Component::Codeblock(_) as self-padding (let is_self_padding = matches!(child.component, Component::Codeblock(_));); every other painter, terminal included, receives a BoxLayout whose height is layout.content_box()'s ch. So a terminal with auto_scroll: false and style.padding: "32px" has 64px less drawable height than the check credits it with: content needing 500px in a 520px border box (456px content box) overflows by 44px and is reported clean. The codeblock arm just above is correct, because codeblock really is handed the border box — so the two arms of the same violation kind need different boxes and currently use the same one.

Fix

Pass the BoxLayout (not a BBox) into check_auto_scroll and compare the terminal's natural height against layout.content_box().3, keeping layout.height for the codeblock arm; add a comment naming is_self_padding as the reason the two differ.

Evidence the audit read

Component::Terminal(t) if !t.auto_scroll => {
    let (_, natural_h) =
        TerminalIntrinsic::from_terminal(t).measure((None, None), max_content);
    if natural_h > bbox.h + 0.5 {

Stacked on fix/geometry-nowrap-height, 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-33).