feat(desktop): add webcam QR code scanning for bunker login

Uses webcam-capture + ZXing to scan QR codes from the camera.
Click the QR icon on the login screen to open a webcam scanner
dialog that auto-detects bunker:// URIs from Amber's QR display.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/auth/LoginCard.kt

@@ -60,8 +60,6 @@ import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
 import org.jetbrains.compose.resources.stringResource
-import javax.swing.JFileChooser
-import javax.swing.filechooser.FileNameExtensionFilter
 
 private val HEX_64_REGEX = Regex("^[0-9a-fA-F]{64}$")
 
@@ -136,33 +134,14 @@ fun LoginCard(
 
                 IconButton(
                     onClick = {
-                        // Try clipboard first, then file picker
-                        val clipboardResult = decodeQrFromClipboard()
-                        if (clipboardResult != null) {
-                            keyInput = clipboardResult
-                            errorMessage = null
-                        } else {
-                            val chooser =
-                                JFileChooser().apply {
-                                    fileFilter =
-                                        FileNameExtensionFilter(
-                                            "Images",
-                                            "png",
-                                            "jpg",
-                                            "jpeg",
-                                            "gif",
-                                            "bmp",
-                                            "webp",
-                                        )
-                                    dialogTitle = "Select QR code image"
-                                }
-                            if (chooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) {
-                                val decoded = decodeQrFromFile(chooser.selectedFile)
+                        scope.launch(Dispatchers.IO) {
+                            val decoded = scanQrFromWebcam()
+                            withContext(Dispatchers.Main) {
                                 if (decoded != null) {
                                     keyInput = decoded
                                     errorMessage = null
                                 } else {
-                                    errorMessage = "No QR code found in image"
+                                    errorMessage = "No QR code found"
                                 }
                             }
                         }

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/auth/QrCodeDecoder.kt

@@ -20,31 +20,23 @@
  */
 package com.vitorpamplona.amethyst.desktop.ui.auth
 
+import com.github.sarxos.webcam.Webcam
+import com.github.sarxos.webcam.WebcamPanel
 import com.google.zxing.BinaryBitmap
 import com.google.zxing.MultiFormatReader
 import com.google.zxing.NotFoundException
 import com.google.zxing.client.j2se.BufferedImageLuminanceSource
 import com.google.zxing.common.HybridBinarizer
-import java.awt.Image
-import java.awt.Toolkit
-import java.awt.datatransfer.DataFlavor
+import java.awt.BorderLayout
+import java.awt.Dimension
 import java.awt.image.BufferedImage
-import java.io.File
-import javax.imageio.ImageIO
+import javax.swing.JDialog
+import javax.swing.JFrame
+import javax.swing.JLabel
+import javax.swing.SwingConstants
+import javax.swing.SwingUtilities
 
-fun decodeQrFromFile(file: File): String? {
-    val image = ImageIO.read(file) ?: return null
-    return decodeQrFromImage(image)
-}
-
-fun decodeQrFromClipboard(): String? {
-    val clipboard = Toolkit.getDefaultToolkit().systemClipboard
-    if (!clipboard.isDataFlavorAvailable(DataFlavor.imageFlavor)) return null
-    val image = clipboard.getData(DataFlavor.imageFlavor) as? Image ?: return null
-    return decodeQrFromImage(image.toBufferedImage())
-}
-
-private fun decodeQrFromImage(image: BufferedImage): String? =
+fun decodeQrFromImage(image: BufferedImage): String? =
     try {
         val source = BufferedImageLuminanceSource(image)
         val bitmap = BinaryBitmap(HybridBinarizer(source))
@@ -53,11 +45,76 @@ private fun decodeQrFromImage(image: BufferedImage): String? =
         null
     }
 
-private fun Image.toBufferedImage(): BufferedImage {
-    if (this is BufferedImage) return this
-    val buffered = BufferedImage(getWidth(null), getHeight(null), BufferedImage.TYPE_INT_ARGB)
-    val g = buffered.createGraphics()
-    g.drawImage(this, 0, 0, null)
-    g.dispose()
-    return buffered
+/**
+ * Opens a modal webcam scanner dialog. Scans frames for QR codes continuously.
+ * Returns decoded text when found, or null if cancelled / no webcam available.
+ * Must be called off the EDT (e.g. from a coroutine on Dispatchers.IO).
+ */
+fun scanQrFromWebcam(): String? {
+    val webcam =
+        try {
+            Webcam.getDefault()
+        } catch (_: Exception) {
+            null
+        } ?: return null
+
+    webcam.viewSize =
+        webcam.viewSizes
+            .filter { it.width <= 1280 }
+            .maxByOrNull { it.width * it.height }
+            ?: webcam.viewSizes.first()
+
+    webcam.open()
+
+    var result: String? = null
+
+    val dialog = JDialog(null as JFrame?, "Scan QR Code", true)
+    dialog.defaultCloseOperation = JDialog.DISPOSE_ON_CLOSE
+    dialog.layout = BorderLayout()
+
+    val panel = WebcamPanel(webcam, false)
+    panel.isFPSDisplayed = false
+    panel.isMirrored = true
+    dialog.add(panel, BorderLayout.CENTER)
+
+    val statusLabel = JLabel("Point camera at QR code...", SwingConstants.CENTER)
+    dialog.add(statusLabel, BorderLayout.SOUTH)
+
+    dialog.preferredSize = Dimension(640, 520)
+    dialog.pack()
+    dialog.setLocationRelativeTo(null)
+
+    // Scanning thread — reads frames and decodes
+    val scanThread =
+        Thread {
+            panel.start()
+            while (result == null && webcam.isOpen && dialog.isVisible) {
+                try {
+                    val image = webcam.image ?: continue
+                    val decoded = decodeQrFromImage(image)
+                    if (decoded != null) {
+                        result = decoded
+                        SwingUtilities.invokeLater { dialog.dispose() }
+                        break
+                    }
+                } catch (_: Exception) {
+                    // webcam may throw during shutdown
+                }
+                Thread.sleep(150)
+            }
+        }
+    scanThread.isDaemon = true
+    scanThread.start()
+
+    // Blocks until dialog is closed (modal)
+    dialog.isVisible = true
+
+    // Cleanup
+    try {
+        panel.stop()
+        webcam.close()
+    } catch (_: Exception) {
+    }
+
+    return result
 }