l0qp1n5qr: Restyle the sign-in screen to the redesign spec

src/styles/signin.css

@@ -0,0 +1,104 @@
+/* Sign-in page (spec "Sign in", ADR 0001). Outside .app: one centered column, no breakpoints.
+   Tokens only, so it follows the active theme (dark by default). */
+.signin {
+  position: relative;
+  min-height: 100vh;
+  overflow: hidden;
+  display: flex;
+  justify-content: center;
+  padding: 28px 24px;
+  background: var(--bg);
+  color: var(--ink);
+}
+.signin-glow {
+  position: absolute;
+  left: 50%;
+  top: -220px;
+  width: 560px;
+  height: 420px;
+  transform: translateX(-50%);
+  border-radius: 50%;
+  background: radial-gradient(ellipse, color-mix(in srgb, var(--accent), transparent 84%), transparent 65%);
+  pointer-events: none;
+}
+.signin-col {
+  position: relative;
+  width: 100%;
+  max-width: 342px;
+  display: flex;
+  flex-direction: column;
+}
+.signin-brand {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: 10px;
+  padding-top: 40px;
+  font-size: 15px;
+}
+.signin-head {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 14px;
+  text-align: center;
+  margin: 72px 0 40px;
+}
+.signin-title {
+  margin: 0;
+  font-family: var(--font-serif), Georgia, serif;
+  font-size: 40px;
+  font-weight: 600;
+  line-height: 1.05;
+  color: var(--ink);
+}
+.signin-title em { font-style: italic; font-weight: 500; }
+.signin-rule {
+  width: 48px;
+  height: 1px;
+  background: linear-gradient(90deg, transparent, color-mix(in srgb, var(--ink), transparent 40%), transparent);
+}
+.signin-form { display: flex; flex-direction: column; gap: 12px; }
+.signin-label {
+  margin: 0;
+  font-size: 11px;
+  font-weight: 700;
+  text-transform: uppercase;
+  letter-spacing: 0.16em;
+  color: var(--ink-3);
+}
+.signin-label-next { margin-top: 6px; }
+.signin-field {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  height: 52px;
+  padding: 0 16px;
+  border-radius: var(--r-ctl);
+  background: var(--tile-2);
+  color: var(--ink-3);
+  box-shadow: inset 0 0 0 1px var(--line-2);
+  transition: box-shadow .25s;
+}
+.signin-field:focus-within {
+  box-shadow: inset 0 0 0 1px color-mix(in srgb, var(--ink), transparent 45%), 0 0 0 4px color-mix(in srgb, var(--ink), transparent 94%);
+}
+.signin-field svg { width: 18px; height: 18px; flex: none; }
+.signin-field input {
+  flex: 1;
+  min-width: 0;
+  height: 100%;
+  margin: 0;
+  padding: 0;
+  border: 0;
+  border-radius: 0;
+  outline: 0;
+  background: transparent;
+  font: inherit;
+  font-size: 15px;
+  color: var(--ink);
+}
+.signin-field input::placeholder { color: var(--ink-3); }
+.signin-form .signin-submit { margin-top: 18px; width: 100%; height: 54px; }
+.signin-form .signin-submit:disabled { opacity: .5; cursor: not-allowed; }
+.signin-error { margin: 0; }