feat: W1 frontend — index.html, style.css, keybar, main.ts (esbuild entry)

- T8 public/index.html      — #term/#keybar, loads ./build/main.js (type=module)
- T9 public/style.css       — fullscreen term, keybar fixed bottom, hidden >768px
- T10 public/keybar.ts      — key→byte map + mountKeybar (13 tests)
- T11 public/main.ts        — xterm+fit, WS client (wss on https/M6), reconnect
                              backoff, resize debounce, mountKeybar wiring

Verified by orchestrator: backend+frontend tsc clean; full suite 141 tests;
npm run build:web bundles main.ts -> public/build/main.js (430kb).
Note: main.ts uses one @ts-ignore for the CSS import (minor; future: *.css d.ts).

public/style.css

@@ -0,0 +1,73 @@
+/* Web Terminal Styling */
+
+/* Full-screen terminal layout */
+html, body {
+  margin: 0;
+  padding: 0;
+  width: 100%;
+  height: 100%;
+  background-color: #1a1a1a;
+  font-family: 'Monaco', 'Menlo', 'Ubuntu Mono', monospace;
+  overflow: hidden;
+}
+
+#term {
+  position: absolute;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 60px;
+  width: 100%;
+  background-color: #1a1a1a;
+  overflow: hidden;
+}
+
+/* Mobile touch keybar — fixed at bottom, horizontal layout */
+#keybar {
+  position: fixed;
+  bottom: 0;
+  left: 0;
+  right: 0;
+  height: 60px;
+  background-color: #2a2a2a;
+  border-top: 1px solid #3a3a3a;
+  display: flex;
+  flex-direction: row;
+  overflow-x: auto;
+  overflow-y: hidden;
+  z-index: 1000;
+  gap: 0;
+}
+
+/* Keybar buttons */
+#keybar button {
+  flex: 1;
+  min-width: 50px;
+  height: 60px;
+  padding: 0;
+  border: 1px solid #444;
+  background-color: #333;
+  color: #ddd;
+  font-size: 12px;
+  cursor: pointer;
+  border-radius: 0;
+  transition: background-color 0.2s;
+  -webkit-user-select: none;
+  user-select: none;
+  -webkit-touch-callout: none;
+}
+
+#keybar button:active {
+  background-color: #555;
+}
+
+/* Hide keybar on desktop (viewport width > 768px) */
+@media (min-width: 769px) {
+  #keybar {
+    display: none;
+  }
+
+  #term {
+    bottom: 0;
+  }
+}