chore: pin Tailwind 4.3.1, which drops module.register() (closes #355)

@tailwindcss/node 4.2.1, loaded by the Tailwind CLI, calls Node's
deprecated module.register() as it starts, so every make build on a
current Node printed the DEP0205 warning. 4.3.1 is the first release that
calls module.registerHooks() instead wherever Node has it.

tailwindcss and @tailwindcss/cli are pinned at exactly 4.3.1, and
yarn.lock carries the new versions of the packages they pull in. The
compiled CSS computes to the same values: it drops the unused .start and
.end rules and writes calc(var(--spacing) * 1) as var(--spacing).

Model: opus-5-5

README.md

@@ -2198,8 +2198,8 @@ Dev dependencies (not shipped in extension):
 | Package            | Version | License | Purpose                   |
 | ------------------ | ------- | ------- | ------------------------- |
 | `esbuild`          | 0.27.3  | MIT     | JS bundler (inlines deps) |
-| `tailwindcss`      | 4.2.1   | MIT     | CSS compilation           |
-| `@tailwindcss/cli` | 4.2.1   | MIT     | Tailwind CLI              |
+| `tailwindcss`      | 4.3.1   | MIT     | CSS compilation           |
+| `@tailwindcss/cli` | 4.3.1   | MIT     | Tailwind CLI              |
 | `jest`             | 30.2.0  | MIT     | Test runner               |
 | `prettier`         | 3.8.1   | MIT     | Code formatter            |