fix(components): resolve default sizes against the node font-size

[LeadcodeDev]

Severity Medium, category correctness. Location: crates/rustmotion-components/src/box_builder.rs:1716

Impact

font_size_px_or goes through Length::px() → px_or_warn, which returns 0.0 for any relative unit; style.rs:1601 asserts this explicitly (assert_eq!(s.font_size_px_or(48.0), 0.0) for "15.6vw"). Five live call sites remain in apply_intrinsic_overrides — List (1498), Callout (1643), Tooltip (1663), PillNav (1688), Marquee (1716) — while every corresponding painter was migrated to the context-aware resolver in the "lot B, wave S" pass (marquee.rs:82 self.style.font_size_px_ctx(&crate::intrinsic::font_size_ctx(...), self.font_size), list.rs:88 the same). So a marquee with "font-size": "2rem" and no explicit style.height gets apply_default_size(css, 800.0, 0.0) → the (false,false) branch writes css.height = Px(0.0) → the node is skipped at paint time and the marquee is invisible; list (1498-1503) collapses to height 0 the same way; callout/tooltip/pill_nav get boxes measured at font-size 0 while the painter draws at the real size, so the ink overflows its own box. intrinsic.rs:27-46 states this wave's goal was to replace font_size_px_or at every site; box_builder was missed, and it is also the one file that does not use the module's own measure_time_font_size_ctx helper (intrinsic.rs:87).

Fix

Replace the five font_size_px_or(...) calls in apply_intrinsic_overrides with font_size_px_ctx(&crate::intrinsic::measure_time_font_size_ctx(0.0), ...), the same helper every *Intrinsic in intrinsic.rs already uses. Add a regression test asserting a marquee/list with "font-size": "2rem" and no explicit height lays out with positive height.

Evidence the audit read

let font_size = m.style.font_size_px_or(m.font_size);
            apply_default_size(css, 800.0, font_size * 2.0);

Based directly on the chantier branch.

Part of the September 2026 audit remediation chantier. Refs #220 (RM-06).