fix(ci): switch to signed IPA build via APPLE_SIGNING group

Replace unsigned CODE_SIGNING_ALLOWED=NO build with proper ad-hoc
signed archive using keychain, certificate, and provisioning profile.
Update xtool.yml schema to match current xtool v1 format.

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

xtool.yml

@@ -1,13 +1,8 @@
 # xTool configuration — https://xtool.sh
-# Run `xtool configure` once to set up your Apple ID credentials and Darwin SDK.
-# Then: `xtool run` to build and install directly to a connected device.
+# Run `xtool setup` once to configure your Apple ID credentials and extract the Darwin SDK.
+# Then: `xtool dev` to build and deploy directly to a connected USB device.
 
-targets:
-  SilverApple:
-    bundleIdentifier: uk.silverlabs.silverapple
-    # Fill in your Apple Developer Team ID (10-char string from developer.apple.com)
-    teamID: ""
-    infoPlist: SilverApple/Info.plist
-    entitlements: SilverApple/SilverApple.entitlements
-    deploymentTarget: "16.0"
-    deviceFamily: [iphone]
+version: 1
+bundleID: uk.silverlabs.silverapple
+infoPath: SilverApple/Info.plist
+entitlementsPath: SilverApple/SilverApple.entitlements