iOS: add fastlane config for TestFlight upload

Adds fastlane Appfile/Fastfile (upload_only lane that pushes an already-
exported IPA to TestFlight via the ASC API key) and the generated README.
The ASC .p8 private key stays outside the repo (~/.appstoreconnect); only
its key_id/issuer_id identifiers are referenced. Gitignores the transient
fastlane/report.xml run artifact.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

iosApp/fastlane/README.md

@@ -0,0 +1,32 @@
+fastlane documentation
+----
+
+# Installation
+
+Make sure you have the latest version of the Xcode command line tools installed:
+
+```sh
+xcode-select --install
+```
+
+For _fastlane_ installation instructions, see [Installing _fastlane_](https://docs.fastlane.tools/#installing-fastlane)
+
+# Available Actions
+
+## iOS
+
+### ios upload_only
+
+```sh
+[bundle exec] fastlane ios upload_only
+```
+
+Upload an already-exported IPA to TestFlight
+
+----
+
+This README.md is auto-generated and will be re-generated every time [_fastlane_](https://fastlane.tools) is run.
+
+More information about _fastlane_ can be found on [fastlane.tools](https://fastlane.tools).
+
+The documentation of _fastlane_ can be found on [docs.fastlane.tools](https://docs.fastlane.tools).