feat(client): implement react frontend application

- Created main entry point `src/client/main.tsx`.
- Created main `App` component `src/client/App.tsx`.
- Implemented state management (`initial`, `waiting`, `success`, `failed`) using `useState`.
- Implemented `handleStart` to call backend `/api/digiid/start` and transition to `waiting` state.
- Implemented `useEffect` hook for polling backend `/api/digiid/status/:sessionId` in `waiting` state.
    - Updates UI state based on polling response (`success`/`failed`).
    - Handles polling errors and cleanup.
- Implemented `handleReset` to return to `initial` state.
- Implemented views for each state:
    - `initial`: Welcome message, Start button.
    - `waiting`: QR code display, status message, Cancel button.
    - `success`: Success message, verified address, address type, Start Over button.
    - `failed`: Failure message, error details, Try Again button.
- Added client-side address type helper `getDigiByteAddressType` in `src/client/utils.ts`.
- Added basic CSS styling in `src/client/index.css` with light/dark mode support.
- Added frontend-related scripts (`dev:frontend`, `dev`, `build`, `lint`, `preview`) to `package.json`.
- Fixed linter type issue with `setInterval` return value.

1 files changed, 115 insertions, 0 deletions

diff --git a/src/client/index.css b/src/client/index.css
new file mode 100644
index 0000000..2349c9b
--- /dev/null
+++ b/src/client/index.css
@@ -0,0 +1,115 @@
+:root {
+  font-family: Inter, system-ui, Avenir, Helvetica, Arial, sans-serif;
+  line-height: 1.5;
+  font-weight: 400;
+  color-scheme: light dark;
+  color: rgba(255, 255, 255, 0.87);
+  background-color: #242424;
+
+  font-synthesis: none;
+  text-rendering: optimizeLegibility;
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}
+
+body {
+  margin: 0;
+  display: flex;
+  place-items: center;
+  min-width: 320px;
+  min-height: 100vh;
+}
+
+#root {
+  max-width: 1280px;
+  margin: 0 auto;
+  padding: 2rem;
+  text-align: center;
+}
+
+.app-container {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 1.5rem;
+}
+
+h1 {
+  font-size: 2.5em;
+  line-height: 1.1;
+  margin-bottom: 1rem;
+}
+
+button {
+  border-radius: 8px;
+  border: 1px solid transparent;
+  padding: 0.6em 1.2em;
+  font-size: 1em;
+  font-weight: 500;
+  font-family: inherit;
+  background-color: #1a1a1a;
+  cursor: pointer;
+  transition: border-color 0.25s;
+}
+button:hover {
+  border-color: #646cff;
+}
+button:focus,
+button:focus-visible {
+  outline: 4px auto -webkit-focus-ring-color;
+}
+button:disabled {
+  background-color: #333;
+  cursor: not-allowed;
+  opacity: 0.6;
+}
+
+.initial-view, .waiting-view, .success-view, .failed-view {
+  padding: 1.5rem;
+  border: 1px solid #555;
+  border-radius: 8px;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 1rem;
+  min-width: 300px;
+}
+
+.waiting-view img {
+  background-color: white; /* Ensure QR code background is white */
+  padding: 10px;
+  border-radius: 4px;
+}
+
+.address {
+  font-family: monospace;
+  background-color: #333;
+  padding: 0.5em;
+  border-radius: 4px;
+  word-break: break-all;
+}
+
+.error-message {
+  color: #ff6b6b;
+  font-weight: bold;
+}
+
+
+@media (prefers-color-scheme: light) {
+  :root {
+    color: #213547;
+    background-color: #ffffff;
+  }
+  button {
+    background-color: #f9f9f9;
+  }
+  .app-container {
+    /* Add light mode adjustments if needed */
+  }
+  .initial-view, .waiting-view, .success-view, .failed-view {
+    border-color: #ccc;
+  }
+  .address {
+     background-color: #eee;
+  }
+} 
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