[wieslawsoltes]

The exact Code OSS Explorer rule sets a generated Seti pseudo-element to font-size: 150% on a 13px label. WebScene retained that parsed number as 150px, so the oversized glyph was clipped by the 22px row and appeared as a path-like block. This change resolves pseudo-element percentage and em font sizes against the originating element's computed size, yielding 19.5px before text measurement and scene serialization.

The existing downloadable-font reftest now covers the exact 13px × 150% case. The native scene gate asserts the serialized 19.5px size while retaining family mutation/restoration, checksum and node identity, 4,096-icon performance/cache/storage, and settled lifecycle coverage.

Evidence:

• Current-main reduced probe: font-size:150% classified supported with stored size 150.
• Exact Chromium test/reference screenshots: byte-identical SHA-256 72959f0a61d3ae7e92e413c3c43a96a366ef35fba6f894d7dd1767978563a867.
• Portable native suite: 40/40 passed.
• Updated WebPlatformSubset manifest lists the reftest successfully.

Closes #417
Parent: #246
Tracking: #235, #259

Excludes #414, #415, #416, and #76.