Add QR code support for Device IDs

- Add printQR() helper function using qrencode
- Display QR code in sync setup for easy mobile pairing
- Add qrencode to doctor dependency check

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cli/grapho.lux

@@ -162,6 +162,18 @@ fn printCmd(cmd: String): Unit with {Process} = {
     ()
 }
 
+// Print a QR code for easy scanning (e.g., device IDs)
+fn printQR(data: String): Unit with {Process} = {
+    if hasCommand("qrencode") then {
+        // Generate small terminal QR code and redirect to stderr
+        let ignore = Process.exec("qrencode -t ANSIUTF8 -m 1 '" + data + "' -o - >&2")
+        ()
+    } else {
+        // Fallback: just show the data
+        printHint("(Install qrencode for QR codes)")
+    }
+}
+
 // =============================================================================
 // Shell helpers
 // =============================================================================
@@ -504,7 +516,9 @@ fn doSyncSetup(): Unit with {Process} = {
             printBold("Your Device ID")
             let ignore = Process.exec("printf '\\033[33m%s\\033[0m\\n' \"" + deviceId + "\" >&2")
             print("")
-            printHint("Share this ID with other devices to pair.")
+            printQR(deviceId)
+            print("")
+            printHint("Scan the QR code or share this ID to pair devices.")
             logEvent("sync", "Device ID displayed")
         } else {
             printStepWarn("Getting device ID", "retry in a moment")
@@ -981,6 +995,12 @@ fn showDoctor(): Unit with {Process} = {
         printStepErr("age", "not found")
     }
 
+    if hasCommand("qrencode") then {
+        printStep("qrencode", "installed")
+    } else {
+        printStepWarn("qrencode", "not found (QR codes disabled)")
+    }
+
     // Directory check
     print("")
     let ignore2 = Process.exec("printf '\\033[2mDirectories:\\033[0m\\n' >&2")