feat: install instruction inside web app

frontend/src/styles/admin-controls.css

@@ -233,6 +233,31 @@
   box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent) 20%, transparent);
 }
 
+.admin-setting-control .admin-setting-json-textarea {
+  min-height: 240px;
+  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", monospace;
+}
+
+.admin-json-toolbar {
+  display: flex;
+  flex: 1 1 100%;
+  align-items: center;
+  gap: 8px;
+}
+
+.admin-json-file-input {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  overflow: hidden;
+  clip: rect(0 0 0 0);
+  white-space: nowrap;
+}
+
+.admin-json-upload {
+  cursor: pointer;
+}
+
 .admin-btn.admin-btn-icon {
   width: 30px;
   height: 30px;

frontend/src/styles/webapp.css

@@ -26,6 +26,33 @@ a {
   padding-bottom: 86px;
 }
 
+.public-install-shell {
+  width: min(100%, 440px);
+  min-height: 100dvh;
+  margin: 0 auto;
+  overflow-x: hidden;
+  padding: max(16px, env(safe-area-inset-top)) max(var(--screen-gutter), var(--safe-inline))
+    max(18px, env(safe-area-inset-bottom)) max(var(--screen-gutter), var(--safe-inline));
+}
+
+.public-install-brand {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  width: 100%;
+  min-height: 48px;
+  box-sizing: border-box;
+  padding: 0 16px;
+  color: var(--text);
+  text-decoration: none;
+}
+
+.public-install-brand strong {
+  color: var(--accent);
+  font-size: 15px;
+  line-height: 1.2;
+}
+
 .loader {
   display: grid;
   min-height: 100dvh;
@@ -2214,6 +2241,26 @@ a {
     margin-right: auto;
   }
 
+  .public-install-shell {
+    width: auto;
+    max-width: none;
+    min-height: 100dvh;
+    margin: 0;
+    overflow-x: visible;
+    padding: max(28px, env(safe-area-inset-top)) var(--desktop-page-gutter) 40px;
+  }
+
+  .public-install-shell > .public-install-brand,
+  .public-install-shell > main {
+    max-width: 1080px;
+    margin-left: auto;
+    margin-right: auto;
+  }
+
+  .public-install-shell > .public-install-brand {
+    width: min(100%, 1080px);
+  }
+
   /* Auth screen: keep it as a focused card in the centre, hide rail. */
   .phone-screen.auth-screen {
     width: min(100%, 460px);