Implement Handler mobile app (React Native + Expo iOS)

Build the committed 2a interactive prototype from Handler Mobile.dc.html as
a real Expo app: six wired screens (Fleet, Agent detail, Answer, Spawn, Log,
Settings) with the exact state logic ported from the design's renderVals().

- Port Leeworks tokens (colors light/dark, typography, spacing, radii,
  shadows) to typed RN values in src/theme.
- Reimplement the design-system components used by the screens (Button,
  Badge, Icon, Switch, Select, TextField, segmented control, chip, tab bar).
- Shared store mirrors the prototype's single-screen navigation and the
  Waiting -> Running flip when agt-7a1d is answered.
- Real OS status bar / home indicator (safe-area insets) replace the mock
  phone chrome; dark mode follows system appearance.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PdF2hHVQ4UUBFPtpeMQ81o

app/src/theme/useTheme.ts

@@ -0,0 +1,17 @@
+import { useColorScheme } from "react-native";
+import { darkColors, lightColors, type ThemeColors } from "./tokens";
+
+export type Scheme = "light" | "dark";
+
+/**
+ * Resolves the active Leeworks palette from the OS appearance.
+ *
+ * The design exposed dark mode as a design-time prop (`data-theme`); on a
+ * real iOS app the faithful equivalent is the system appearance, so the
+ * theme follows `useColorScheme()` (app.json sets userInterfaceStyle
+ * "automatic"). All six screens read colors through this hook.
+ */
+export function useTheme(): { colors: ThemeColors; scheme: Scheme } {
+  const scheme: Scheme = useColorScheme() === "dark" ? "dark" : "light";
+  return { colors: scheme === "dark" ? darkColors : lightColors, scheme };
+}