feat: complete AutoFill target capability wiring

Adds App Groups + Keychain Sharing entitlements to the AutoFill
target (matching the main app's group.org.antiloop222.mypass /
org.antiloop222.mypass), sets REGISTER_APP_GROUPS so automatic
signing registers the capability, and links MyPassCore as a
framework dependency by reusing the existing local package product
reference. Verified with `xcodebuild -scheme AutoFill build` for the
iOS Simulator: the AutoFill.appex target builds, signs, and embeds
cleanly (the only build failure is the pre-existing, expected
ContentView.swift/Item SwiftData breakage in the MyPass app target,
unrelated to this change).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WYqycDFsynHH9VnnK7LNSf

MyPass.xcodeproj/xcuserdata/kriss.xcuserdatad/xcschemes/xcschememanagement.plist

@@ -7,12 +7,12 @@
 		<key>AutoFill.xcscheme_^#shared#^_</key>
 		<dict>
 			<key>orderHint</key>
-			<integer>1</integer>
+			<integer>4</integer>
 		</dict>
 		<key>MyPass.xcscheme_^#shared#^_</key>
 		<dict>
 			<key>orderHint</key>
-			<integer>0</integer>
+			<integer>3</integer>
 		</dict>
 	</dict>
 </dict>