refactor(host): rename the directory-picker dialog backend and kind to native

The browse interaction also presents a dialog (the in-app modal), so 'dialog'
failed to discriminate the two capability kinds; 'native' names where the
chooser runs. Package directory-picker-dialog -> directory-picker-native, kind
'dialog' -> 'native', with every seam/gateway/client/doc reference updated and
the seam Agent Note's naming rationale rewritten to match.

packages/host/directory-picker-native/src/index.ts

@@ -0,0 +1,33 @@
+/**
+ * Native backend of the directory-picker seam: registers `ctx.directoryPicker`
+ * with the `native` capability, opening one native OS chooser on the host
+ * display per pick (macOS `osascript`, Windows STA PowerShell
+ * `FolderBrowserDialog`, Linux Zenity with a KDialog fallback). Only viable
+ * when the operator sits at the host's screen; remote deployments compose the
+ * browse backend instead.
+ * @module @deepseek-ai/dsh-host-directory-picker-native
+ */
+
+import { DirectoryPicker } from '@deepseek-ai/dsh-host-directory-picker'
+import type { DirectoryPickerCapability } from '@deepseek-ai/dsh-host-directory-picker'
+import { pickNativeDirectory } from './native-picker.ts'
+
+export type { DirectoryPickerInternals, DirectoryPickerRunner } from './native-picker.ts'
+export { pickNativeDirectory } from './native-picker.ts'
+
+/** The `ctx.directoryPicker` native implementation (stable capability object per service life). */
+export default class NativeDirectoryPicker extends DirectoryPicker {
+  private readonly nativeCapability: DirectoryPickerCapability = {
+    kind: 'native',
+    /* v8 ignore next -- pure forward to pickNativeDirectory (its spec owns behavior); invoking here opens a real chooser. */
+    pick: signal => pickNativeDirectory(signal),
+  }
+
+  /**
+   * The native interaction capability.
+   * @returns the stable `native` capability object.
+   */
+  capability(): DirectoryPickerCapability {
+    return this.nativeCapability
+  }
+}