Move tailwind off the deprecated module.register() (closes #32)

Frontend builds on Node 26 or newer, such as make test on a host with
Node 26, printed Node's DEP0205 warning; the build in Dockerfile runs on
Node 22, which never printed it. The trace names @tailwindcss/node,
which @tailwindcss/vite brings in at its own exact version; tailwind
4.3.1 calls module.registerHooks() where Node has it. @tailwindcss/vite
and tailwindcss move to 4.3.3, inside the ranges package.json already
allows, so only yarn.lock changes, every entry still with an integrity
hash. tailwindcss moves too so that one tailwind version is installed.

Model: opus-5-5

TODO.md

@@ -23,6 +23,18 @@ latest run passes.
 
 # Completed Steps
 
+- 2026-10-04: a frontend build on Node 26 or newer, such as `make test` on a
+  host with Node 26, no longer prints Node's warning that `module.register()` is
+  deprecated (issue #32); the build in `Dockerfile` runs on Node 22, which never
+  printed it. The call was in `@tailwindcss/node`, which `@tailwindcss/vite`
+  brings in at its own exact version; tailwind 4.3.1 calls
+  `module.registerHooks()` instead where Node has it. `yarn.lock` now has
+  `@tailwindcss/vite` and `tailwindcss` at 4.3.3, inside the ranges
+  `package.json` already allowed, and tailwind's own dependencies moved with
+  them. The built CSS changes only in how it is written out, in tailwind's
+  Firefox focus-ring rule, which no longer applies to iframes (the page has
+  none, so nothing on it looks different), and in tailwind's default sans-serif
+  font list, which the page does not use: `body` sets a monospace font
 - 2026-10-03: the frontend's unit tests cover what the page computes (issue
   #21): `humanDuration`, the latency colours of a figure and of a sparkline
   either side of each boundary, a target's min, max, average and median latency