fix(compiler): read a media query's em and rem against the font size rem inlines

[YevheniiKotyrlo]

Problem

A media query has no element, so its em and its rem are both the initial font size (Media Queries 4 §1.3). The compiler keeps a media bound in em as a runtime em descriptor, and with inlineRem: false a bound in rem as a runtime rem descriptor, and the media evaluator decides neither: (min-width: 10em) never matches, and with inlineRem: false no rem breakpoint does - Tailwind 4's sm: to 2xl: among them.

Solution

The compiler reads a media bound in em or rem against the rem it inlines, or React Native's default font size when inlineRem is false, so the bound is a number before the evaluator sees it. Container queries keep their em, which is the container's.

That default font size was a literal 14 in five places - the compiler's fallback, parseLength's default, the runtime's seed of __rn-css-rem, the runtime's default fontSize, and an unread rem field on the builder - and is DEFAULT_REM in src/utilities/rem.ts now; the unread field goes.

Tests

src/__tests__/native/media-query-font-relative.test.tsx renders a min-width and a max-width query at each bound - in em, against an inlined rem of 16, and in em and rem with inlineRem: false - and an em range. All six fail on #426.

Verification

On Ubuntu with the workflow's steps - build, lint, typecheck, yarn test, node --test node/__tests__/*.mjs, both library builds, the web export, the unstaged-changes checks and commitlint - everything passes.

Not run: the iOS and Android example builds.

Unchanged: an em inside a calc() in a media query is still a runtime descriptor the evaluator answers as unknown.

Device evidence, before and after: #494 (comment)

Merge order

It carries #426's commits and changes the media operand parsing #426 adds, so #426 lands first.

It also shares lines with #388 (compiler/media-query.ts, native/conditions/media-query.ts), #389 (compiler/declarations.ts, utilities/index.ts), #391 (compiler/declarations.ts, utilities/index.ts), #392 (native-internal/root.ts), #410 (native-internal/root.ts), #412 (native-internal/root.ts), #413 (compiler/declarations.ts), #415 (native/conditions/media-query.ts), #417 (compiler/declarations.ts), #420 (compiler/declarations.ts, utilities/index.ts), #425 (native/conditions/media-query.ts), #459 (compiler/compiler.types.ts, native/conditions/media-query.ts), #460 (compiler/compiler.ts), #491 (compiler/declarations.ts, utilities/index.ts), #492 (compiler/declarations.ts, utilities/index.ts), #495 (compiler/declarations.ts, utilities/index.ts); whichever lands second rebases.

[YevheniiKotyrlo]

Device evidence — before / after

UNFIXED — Only the control paints. A bound in em is left for the runtime, which cannot decide it, so neither em query ever matches.

FIXED — All three bars paint green. A media query's em is the initial font size, so 10em is 160 pixels and 1000em is wider than any screen.

before — 3.1.0-rc.0	after — with this PR

Android 16 emulator (API 36, GLES on the host GPU), 1140×2400 @ 480dpi, both frames from one run. My test app inlines rem at 16px, so the em bounds read 160px and 16000px. before is the published 3.1.0-rc.0 plus what my test app needs from my other patches to run: the native and native-internal subpath exports, PR 459, cascade-layer ranking, and a shim that compiles a class-qualified :root inert. after adds the rest of my open PRs, this one included. One of them shows on every screen: PR 417 narrows a var()-valued font-family to one family, so the after sets its text in the theme's face where the before falls back to the platform's.