Measure the screen, then decide what fits on it

The ride screen was built for a 1440x900 window and expressed its type
scale in vw. On a phone that fails twice over: 7vw of a 412px viewport is
29px, well under what is readable from the bars, and five side-by-side
readouts do not fit across 412px at any type size. Shrinking is not the
answer to a small screen — showing less is (FR-9.17, FR-9.18).

So screen size becomes a measured input. viewport.ts is a pure function
from a measurement — width, height, DPR, whether the pointer is coarse —
to a layout plan: type sizes in pixels, column counts, and which sections
earn their space. viewport.svelte.ts measures and publishes it as CSS
custom properties and data-* attributes; the stylesheets read those. The
three max-width media queries are gone, so there is now exactly one
definition of "narrow" in the codebase rather than four that can disagree
about where a phone starts.

The sizes are absolute rather than relative, and that is a physical
argument, not a preference. A number has to subtend enough visual angle
to read from the riding position. Desktop is ~96 CSS px per inch at about
a metre; Android's CSS pixel is the dp, ~160 per inch, and a bar-mounted
phone sits at roughly 0.6 m. (160/96) x (0.6/1.0) is almost exactly 1, so
the same pixel size is about as readable in both places — which is why
the floors are plain numbers with no per-platform correction, and why a
small screen is a content problem.

What gets dropped, and in what order: anything the rider cannot act on
mid-ride goes before anything they can. Sparklines first — they are
history, and a 60px chart is a smear. Then average / normalised / work /
burned, which is what the summary screen is for. The detail row survives
longer, because "climbing left" is the question a rider on a hill is
actually asking, and elapsed time stays on a phone while covered and
ascended go. The route profile is the screen's whole point (FR-9.7) and
goes only in landscape on a phone, where keeping it would leave nothing
for the numbers.

Touch is treated as an input, not a narrower mouse (FR-9.19): 48px
targets, hover styling suppressed so it does not stick after a tap, and
keyboard hints hidden — with a word added to the help button, which
carried only a key cap and would otherwise have become unpressable.

Being a pure function is the point: "does this fit on a Pixel 7" is now
answerable in CI on a machine with no phone attached. 15 tests, run by
`npm --prefix ui test`.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ui/package.json

@@ -7,7 +7,9 @@
     "dev": "vite",
     "build": "vite build",
     "check": "svelte-check --tsconfig ./tsconfig.json",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "test": "vitest run",
+    "test:watch": "vitest"
   },
   "dependencies": {
     "@tauri-apps/api": "^2.9.0",
@@ -21,7 +23,8 @@
     "svelte-check": "^4.1.4",
     "tslib": "^2.8.1",
     "typescript": "^5.7.3",
-    "vite": "^6.0.11"
+    "vite": "^6.0.11",
+    "vitest": "^4.1.10"
   },
   "allowScripts": {
     "esbuild@0.25.12": true