fix: preserve integer text advances and inside stroke geometry

[owjs3901]

The narrowest width of a screen diverged from Figma's own PNG six times worse than the widest one. Two separate defects were compounding; both are fixed here. Measured on landing against Figma's reference PNG:

Screen	Width	Before	After
landing-833-3640	360	11.41%	4.99%
landing-833-3322	992	3.10%	2.47%
landing-832-2975	1920	1.84%	1.50%

The rendered height now equals the design height at all three widths. Thresholds moved down only.

1. The line advance was a ratio

Figma advances each line by round(fontSize x ratio); the browser accumulates the fraction. A ratio structurally cannot express an integer advance across several font sizes, which is why the sign of the error flipped with font size (38/18/28 too tall, 52/36 too short) and every uniform correction traded one width for another. The advance is now emitted as a whole-pixel length, and all seven measured text blocks match their design height exactly.

A pixel advance is only valid for the size it was computed from, so the resolved font size travels with it. A percentage line height whose font size is missing or bound to a mode-dependent variable is refused with a typed error naming the node or text style, rather than emitted as a number that would be wrong at another size.

2. An inside stroke was taking layout space

Figma's inside stroke consumes no layout space. With box-sizing: border-box a CSS border eats into the content box, and the existing padding compensation cannot absorb it when the design's own padding is narrower than the stroke - padding cannot go negative. Every bordered auto-layout container therefore grew by twice its stroke weight and pushed everything below it down by exactly 2px, at every width.

That case now paints inward with outline at a negative offset, which takes no layout space, and the padding compensation stands down for it. The decision keys on stroke alignment, layout mode, and stroke weight against padding - never on a viewport width - so it survives a design redrawn at another size.

Corpus and provenance

Twenty-four plugin goldens change, each enumerated with its reason in docs/line-box-displacement.md. Forty-seven of the forty-eight line-height changes are the ratio-to-integer conversion (1.6 to 26px); the remaining one is a node whose typography token previously suppressed its own resolved metrics. The corpus consistency test and manifest checksums are unchanged in force.

Source map and provenance follow the emission: outline/outlineOffset carry their stroke provenance, and a rich-text wrapper's own advance is attributed to the segment whose text follows it.

Verification

Re-measured independently from this branch with a binary built here (a9b96f24df75, SHA-256 1859B639...), not from the worker's report: python scripts/acquire.py landing then node scripts/render.mjs exits 0 against the tightened thresholds.

Gates: fmt 0, clippy --locked --workspace --all-targets --all-features -D warnings 0, cargo test --workspace 1056 passed / 0 failed / 2 ignored, insta --check no drift, stdio_smoke 2 passed.