UI: light Things-3 design system — tokens, task rows, chips, home

Replaces the dark navy palette with a light grouped-background system:
- theme.ts: full token set (space/radius/type/shadow) + light+dark palettes
- ui.tsx: Screen/Title/SectionHeader/Card/Separator/Pill/Empty primitives
- TaskRow: rounded-square checkbox carrying priority colour, inset separators
- TaskListScreen: rows grouped into a card, drag lift, refined deferred footer
- Icon.tsx: dependency-free geometric icon set (emoji don't take a tint)
- home: large title, Next-up card, "needs attention" rows, icon tab bar
- Priority/Estimate/Date chips unified on the accent-soft active state

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/src/lib/theme.ts

@@ -1,12 +1,115 @@
-export const C = {
-  bg: "#0F1115",
-  surface: "#1A1D24",
-  surface2: "#232733",
-  border: "#2C313D",
-  text: "#E6E8EC",
-  muted: "#8A909C",
-  accent: "#5B8DEF",
-  done: "#4CAF7D",
-  danger: "#E05B5B",
-  warn: "#E0A93E",
+// Design tokens.
+//
+// The look is modelled on Things 3: a light, calm canvas, generous whitespace,
+// hairline inset separators instead of boxes, and exactly one accent colour
+// used sparingly. Everything visual in the app resolves through this file —
+// no component hard-codes a hex value (priority flags are the one exception,
+// and they live in `priority.ts` alongside their labels).
+
+/** Named palette. `dark` is complete and ready to wire to a theme toggle. */
+const light = {
+  /** Screen background behind grouped content. */
+  bg: "#F7F7F9",
+  /** Card / row surface that sits on `bg`. */
+  surface: "#FFFFFF",
+  /** Inputs, pressed states, subtle fills. */
+  surface2: "#EFEFF3",
+  /** Card outline. Deliberately barely-there. */
+  border: "#E6E6EB",
+  /** Inset hairline between rows inside a card. */
+  separator: "#ECECF0",
+  /** Primary reading colour. Near-black, never pure #000. */
+  text: "#16161A",
+  /** Supporting copy that should still be comfortably readable. */
+  textSecondary: "#6E6E76",
+  /** Metadata, placeholders, de-emphasised chrome. */
+  muted: "#9A9AA2",
+  accent: "#2F6FED",
+  /** Tinted accent wash for selected chips and active states. */
+  accentSoft: "#E8F0FE",
+  done: "#2FA36B",
+  danger: "#E5484D",
+  warn: "#D98324",
+  /** Text that sits on top of `accent`. */
+  onAccent: "#FFFFFF",
+} as const;
+
+const dark = {
+  bg: "#0C0C0F",
+  surface: "#17171B",
+  surface2: "#212127",
+  border: "#2A2A31",
+  separator: "#26262C",
+  text: "#F2F2F5",
+  textSecondary: "#A6A6B0",
+  muted: "#7A7A85",
+  accent: "#4C86F0",
+  accentSoft: "#1B2740",
+  done: "#3FBF84",
+  danger: "#F0605F",
+  warn: "#E0A93E",
+  onAccent: "#FFFFFF",
+} as const;
+
+export const PALETTES = { light, dark } as const;
+
+/**
+ * Active palette. Styles are created at module scope (StyleSheet.create) so
+ * this is a static choice rather than a hook — switching themes at runtime
+ * would mean moving every stylesheet inside its component.
+ */
+export const C = light;
+
+/** 4pt spacing grid. Screen gutter is `space.lg`. */
+export const space = {
+  xs: 4,
+  sm: 8,
+  md: 12,
+  lg: 16,
+  xl: 20,
+  xxl: 28,
+} as const;
+
+export const radius = {
+  sm: 8,
+  md: 12,
+  /** Cards and grouped lists. */
+  lg: 16,
+  /** Chips and pills. */
+  pill: 999,
+} as const;
+
+/**
+ * Type scale. `title` is the large in-content screen heading that replaces a
+ * cramped nav-bar title; `row` is the task title size — 17pt, matching the
+ * platform body size Things and Todoist both settle on.
+ */
+export const type = {
+  title: { fontSize: 30, fontWeight: "700", letterSpacing: -0.6 },
+  section: { fontSize: 13, fontWeight: "600", letterSpacing: 0.3 },
+  row: { fontSize: 17, letterSpacing: -0.2 },
+  body: { fontSize: 15 },
+  meta: { fontSize: 13 },
+  chip: { fontSize: 14, fontWeight: "500" },
+} as const;
+
+/**
+ * Card elevation. Kept extremely soft — a Things-like surface reads as paper,
+ * not as a floating panel.
+ */
+export const shadow = {
+  card: {
+    shadowColor: "#0B0B12",
+    shadowOpacity: 0.05,
+    shadowRadius: 10,
+    shadowOffset: { width: 0, height: 2 },
+    elevation: 1,
+  },
+  fab: {
+    shadowColor: "#0B0B12",
+    shadowOpacity: 0.22,
+    shadowRadius: 14,
+    shadowOffset: { width: 0, height: 6 },
+    elevation: 6,
+  },
 } as const;