Add explicit scheme so the share extension is part of the build

Without an explicit scheme, xcodebuild's auto-scheme only reports the
app target's settings — which made the Mac mini builder skip the share
extension when generating provisioning profiles, causing the export to
fail with "GiteaIssueShare.appex requires a provisioning profile."

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

project.yml

@@ -50,3 +50,14 @@ targets:
         CODE_SIGN_ENTITLEMENTS: GiteaIssueShare/GiteaIssueShare.entitlements
         TARGETED_DEVICE_FAMILY: "1,2"
         SKIP_INSTALL: YES
+
+schemes:
+  GiteaIssue:
+    build:
+      targets:
+        GiteaIssue: all
+        GiteaIssueShare: all
+    run:
+      config: Debug
+    archive:
+      config: Release