fix(app): unstick iOS image picker and land reusable Maestro primitives

On iOS, tapping "+" → "Add image" in the Composer left an invisible
backdrop trapping touches after the native photo picker dismissed. Root
cause: the dropdown menu's onSelect fired while the RN Modal was still
completing UIKit dismissal, so PHPicker presented over a dismissing
Modal that never cleanly released.

DropdownMenu now defers the selected item's onSelect until Modal
onDismiss (UIKit-level completion) plus a short buffer on iOS, then
invokes it. Same DropdownMenu instance — no per-call opt-in.

Along the way, the Maestro repro surfaced a controlled-TextInput
character-drop race: fast inputText on a controlled input drops
characters mid-type. Direct-host and pair-link inputs are now
ref-backed uncontrolled inputs with stable testIDs.

New reusable E2E primitives under packages/app/maestro/:
- flows/land-in-chat.yaml — clearState + direct connect to
  127.0.0.1:6767, lands in the composer. Compose on this for any
  composer-level fixture.
- image-picker-repro.yaml — regression for the zombie-backdrop bug.

docs/MOBILE_TESTING.md gains the patterns: reach-the-composer via
land-in-chat, uncontrolled inputs for Maestro-typed fields, and the
dropdown → native-presenter dismissal timing on iOS.

Existing relay-pairing and relay-then-direct fixtures updated to use
stable testIDs instead of ambiguous text / point-based taps.

packages/app/src/components/add-host-method-modal.tsx

@@ -71,6 +71,7 @@ export function AddHostMethodModal({
         style={styles.option}
         onPress={handleDirect}
         accessibilityLabel="Direct connection"
+        testID="add-host-method-direct"
       >
         <Link2 size={18} color={theme.colors.foreground} />
         <View style={styles.optionBody}>
@@ -93,6 +94,7 @@ export function AddHostMethodModal({
         style={styles.option}
         onPress={handlePaste}
         accessibilityLabel="Paste pairing link"
+        testID="add-host-method-pair-link"
       >
         <ClipboardPaste size={18} color={theme.colors.foreground} />
         <View style={styles.optionBody}>