fix(ios): wire Wi-Fi config characteristic + actually push creds on Confirm

[Flo5k5]

Two stub-level gaps in the open-source app prevented the pairing from
ever completing:

1. AppState.swift never maps the E2E5E5E3 (Config) characteristic to
   BlufiUtil.writeWifiSetCharacteristic. Without the mapping, any
   attempt to sendWifiSetData() early-returns with "No writable
   characteristic".

2. BindingDevice.confirmWifi() only flipped the pairingStatus to
   DistributionNetwork and then ChangeTheName after a 1s delay,
   without ever writing anything over BLE. The firmware never
   received the Wi-Fi credentials, the StackChan stayed offline.

Fix:

• Assign writeWifiSetCharacteristic when the E2E5E5E3 characteristic
  is discovered during the GATT service scan.
• Serialise {"ssid":..., "password":...} as JSON in confirmWifi and
  send it via BlufiUtil.sendWifiSetData before animating the UI
  progression. The firmware handler (hal_ble.cpp:
  _handle_ble_config_write) parses this exact shape.

Both fixes live on self-host for now; they should also land upstream.

[Flo5k5]

Hi 👋 — closing this PR as fixed-by-replacement. The upstream merged commit e8b9973 ("prepare v1.1.4 release with native bridge and stability cleanups" #38) completely replaced the native SwiftUI iOS app with a Flutter app. The Swift file(s) this PR patches (app/StackChan/*.swift) have been deleted upstream and replaced by app/lib/*.dart + app/ios/Runner/*.swift (Flutter native bridge). The patch is no longer applicable as-is.

I've preserved the Swift-based patches on a dedicated branch legacy/swift-ios on my fork, in case the underlying fix logic can be ported to the Flutter codebase later (BLE scan trigger, dual UUID scan, Wi-Fi push on Confirm, online/offline bool swap).

Happy to re-open or re-submit against the Flutter codebase if useful. Thanks for the review on the merged firmware PRs (#20/#21/#24) 🙏