Add a curl/wget one-line installer and popup setup detection

Add install-remote.sh, which fetches the latest release and runs its
install.sh so setup no longer needs a git clone. The popup now probes
the native host with a "ping" action on open and, if it's not
registered yet, shows the one-liner (with copy-to-clipboard) instead
of the auto-capture toggle -- so a Web Store install can be completed
end-to-end by clicking the extension icon and pasting one command.

extension/popup.js

@@ -1,13 +1,60 @@
+const NATIVE_HOST = "com.kget_capture.host";
+const INSTALL_COMMAND =
+  "curl -fsSL https://raw.githubusercontent.com/andwati/kget-capture/main/install-remote.sh | bash";
+
+const setupPanel = document.getElementById("setup-needed");
+const readyPanel = document.getElementById("ready");
 const checkbox = document.getElementById("auto-capture-toggle");
 const statusLine = document.getElementById("status-line");
+const copyFeedback = document.getElementById("copy-feedback");
 
 function renderStatus(enabled) {
   statusLine.textContent = `Auto-capture: ${enabled ? "ON" : "OFF"}`;
 }
 
-chrome.storage.local.get({ autoCaptureEnabled: true }).then(({ autoCaptureEnabled }) => {
-  checkbox.checked = autoCaptureEnabled;
-  renderStatus(autoCaptureEnabled);
+function showReady() {
+  setupPanel.hidden = true;
+  readyPanel.hidden = false;
+  chrome.storage.local.get({ autoCaptureEnabled: true }).then(({ autoCaptureEnabled }) => {
+    checkbox.checked = autoCaptureEnabled;
+    renderStatus(autoCaptureEnabled);
+  });
+}
+
+function showSetupNeeded() {
+  document.getElementById("setup-command").textContent = INSTALL_COMMAND;
+  readyPanel.hidden = true;
+  setupPanel.hidden = false;
+}
+
+// The native host is only reachable once install.sh (or install-remote.sh)
+// has registered it -- sendNativeMessage fails with a lastError like
+// "Specified native messaging host not found" until then, which is exactly
+// the signal we want to gate the rest of the popup on.
+function checkNativeHost() {
+  chrome.runtime.sendNativeMessage(NATIVE_HOST, { action: "ping" }, () => {
+    if (chrome.runtime.lastError) {
+      showSetupNeeded();
+    } else {
+      showReady();
+    }
+  });
+}
+
+checkNativeHost();
+
+document.getElementById("recheck-setup").addEventListener("click", checkNativeHost);
+
+document.getElementById("copy-command").addEventListener("click", async () => {
+  try {
+    await navigator.clipboard.writeText(INSTALL_COMMAND);
+    copyFeedback.textContent = "Copied to clipboard.";
+  } catch (e) {
+    copyFeedback.textContent = "Couldn't copy -- select and copy the command manually.";
+  }
+  setTimeout(() => {
+    copyFeedback.textContent = "";
+  }, 2000);
 });
 
 checkbox.addEventListener("change", () => {