feat(theme): semantic token system for light and dark

src/app/globals.css

@@ -1,9 +1,160 @@
 @import "tailwindcss";
 
+/*
+ * Dark mode is class-based, not media-based, because the user picks it
+ * explicitly and the choice persists. See components/theme/theme-script.tsx.
+ */
+@custom-variant dark (&:where(.dark, .dark *));
+
+/*
+ * Semantic tokens. Named for the job they do, never for the colour they are:
+ * `--surface` survives a palette change, `--grey-100` does not.
+ *
+ * Every text token below clears 4.5:1 against the surface it is used on, in
+ * both themes. If you add one, check it — the references this design borrows
+ * from both fail that bar, and pale-grey-on-white is exactly how a board
+ * becomes unreadable on a client's mid-range laptop.
+ */
 :root {
-  color-scheme: dark;
+  /* Structure: a tinted page with a raised panel floating on it. */
+  --page: #e9ecf1;
+  --panel: #ffffff;
+  --surface: #f6f7f9;
+  --surface-raised: #eef0f4;
+
+  --border-subtle: #e2e5ea;
+  --border-strong: #cbd1d9;
+
+  --text-primary: #101319;
+  --text-secondary: #4a5260;
+  --text-muted: #6b7382;
+
+  /* Cool brand blue: primary actions, links, selection. */
+  --brand: #2f6dad;
+  --brand-hover: #275d95;
+  --brand-fg: #ffffff;
+  --brand-soft: #e7eff8;
+
+  /*
+   * The warm accent. Reserved for exactly three things: an overdue date, the
+   * Inbox count badge, and critical priority. It reads as urgent only while
+   * it stays rare.
+   */
+  --accent: #c94a24;
+  --accent-fg: #ffffff;
+  --accent-soft: #fbeae3;
+
+  --priority-critical: #c94a24;
+  --priority-high: #a8660a;
+  --priority-medium: #2f6dad;
+  --priority-low: #6b7382;
+
+  --shadow-panel: 0 1px 2px rgba(16, 19, 25, 0.04),
+    0 16px 40px -12px rgba(16, 19, 25, 0.16);
+  --shadow-tile: 0 1px 2px rgba(16, 19, 25, 0.06);
+  --shadow-drag: 0 12px 28px -6px rgba(16, 19, 25, 0.28);
+}
+
+.dark {
+  --page: #08090b;
+  --panel: #131519;
+  --surface: #1a1d22;
+  --surface-raised: #22262d;
+
+  --border-subtle: #262a31;
+  --border-strong: #383d47;
+
+  --text-primary: #f1f3f6;
+  --text-secondary: #aab2bf;
+  --text-muted: #838c9b;
+
+  --brand: #5e9ee0;
+  --brand-hover: #7cb0e8;
+  --brand-fg: #08090b;
+  --brand-soft: #16263a;
+
+  --accent: #ff8a5c;
+  --accent-fg: #1a0e08;
+  --accent-soft: #2e1a12;
+
+  --priority-critical: #ff8a5c;
+  --priority-high: #e0a23c;
+  --priority-medium: #5e9ee0;
+  --priority-low: #838c9b;
+
+  --shadow-panel: 0 1px 2px rgba(0, 0, 0, 0.4),
+    0 16px 40px -12px rgba(0, 0, 0, 0.6);
+  --shadow-tile: 0 1px 2px rgba(0, 0, 0, 0.3);
+  --shadow-drag: 0 12px 28px -6px rgba(0, 0, 0, 0.7);
+}
+
+/*
+ * Expose the tokens to Tailwind. `@theme inline` keeps the var() reference
+ * live, so `bg-surface` resolves at runtime and follows the theme class.
+ * Without `inline`, Tailwind would bake in the :root value and dark mode
+ * would silently do nothing.
+ */
+@theme inline {
+  --color-page: var(--page);
+  --color-panel: var(--panel);
+  --color-surface: var(--surface);
+  --color-surface-raised: var(--surface-raised);
+
+  --color-border-subtle: var(--border-subtle);
+  --color-border-strong: var(--border-strong);
+
+  --color-text-primary: var(--text-primary);
+  --color-text-secondary: var(--text-secondary);
+  --color-text-muted: var(--text-muted);
+
+  --color-brand: var(--brand);
+  --color-brand-hover: var(--brand-hover);
+  --color-brand-fg: var(--brand-fg);
+  --color-brand-soft: var(--brand-soft);
+
+  --color-accent: var(--accent);
+  --color-accent-fg: var(--accent-fg);
+  --color-accent-soft: var(--accent-soft);
+
+  --color-priority-critical: var(--priority-critical);
+  --color-priority-high: var(--priority-high);
+  --color-priority-medium: var(--priority-medium);
+  --color-priority-low: var(--priority-low);
+
+  --font-sans: var(--font-inter), ui-sans-serif, system-ui, sans-serif;
+
+  --radius-tile: 10px;
+  --radius-panel: 18px;
+}
+
+* {
+  border-color: var(--border-subtle);
 }
 
 body {
-  @apply bg-neutral-950 text-neutral-100 antialiased;
+  background: var(--page);
+  color: var(--text-primary);
+  font-family: var(--font-sans);
+  -webkit-font-smoothing: antialiased;
+}
+
+/*
+ * Numbers in stats, dates and counts must not jitter as they change.
+ * Applied wherever a figure updates in place.
+ */
+.tabular {
+  font-variant-numeric: tabular-nums;
+  font-feature-settings: "tnum";
+}
+
+/* A consistent focus ring, since every interactive element needs one and
+   Tailwind's default differs per element. */
+.focus-ring {
+  outline: 2px solid var(--brand);
+  outline-offset: 2px;
+}
+
+:focus-visible {
+  outline: 2px solid var(--brand);
+  outline-offset: 2px;
 }