feat(theme): Light/Dark/System, reduced motion, and one radius scale

The theme foundation DESIGN.md requires (ADR 0060):

- A design token may carry a `dark` value and a `reduced` value. The
  token stylesheet selects them in CSS alone: dark under
  prefers-color-scheme unless the host chose light, or when it chose
  dark; motion durations zero under prefers-reduced-motion unless it
  allowed motion, or when it chose reduce. `color-scheme` travels with
  the tokens. System is live, an explicit choice wins, and every module
  root follows through custom-property inheritance, with no module
  contract change.
- @ekklesia/design-tokens adds a small appearance API: system/light/dark
  and system/reduce/allow, parsers for untrusted stored values,
  resolvers, and a controller that applies the attributes immediately.
  The shell applies it before React renders. That is the hook the
  account preferences work will feed; nothing is persisted. The
  Dashboard page declares `color-scheme: light dark` so a dark system
  never flashes white. Displays stay light.
- A designed dark theme: teal-tinted charcoal, never pure black or
  white, the same teal accent.
- WCAG AA contrast is tested for 41 element pairings in both schemes.
  Two light pairings failed and are fixed visibly: text.muted darkens,
  and form controls get a new border.control (3:1).
  background.placeholder keeps skeletons visible in dark.
- Motion tokens (duration-short, duration-ambient) replace literal
  durations and every per-element reduced-motion rule. radius.scale
  multiplies sm/md/lg, unchanged at its default of 1.
- The sign-in card and module loading/error text move from literal
  colours to tokens. Guards keep raw colours and literal radii out of
  Dashboard product source and @ekklesia/ui.
- Fixes ConfirmationDialog's phrase input, which used a class that
  does not exist (`ek-input`) and so was unstyled.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

surfaces/shell/tests/dashboard-assets.test.ts

@@ -34,6 +34,15 @@ describe("Dashboard host asset locator", () => {
     expect(rootSource).not.toContain("dashboard-assets");
   });
 
+  it("declares both colour schemes before any script runs, and takes its background from tokens", async () => {
+    // So a dark system never flashes a white page while the shell loads (ADR 0060).
+    const html = await readFile(path.join(packageDirectory, "index.html"), "utf8");
+
+    expect(html).toContain('<meta content="light dark" name="color-scheme" />');
+    expect(html).toContain("background: var(--ekklesia-background-page);");
+    expect(html).toContain("color: var(--ekklesia-text-primary);");
+  });
+
   it("loads exactly one fixed, absolute, same-origin script and no inline script", async () => {
     const html = await readFile(path.join(packageDirectory, "index.html"), "utf8");