Run tests in CI on Linux

Adds a Gitea Actions workflow running swift test in a swift:6.2 container.

The kit did not build without Apple frameworks, so the two files that need
them are wrapped in #if canImport, and the SwiftUI app target is added to
Package.swift only on macOS. Neither can exist in a Linux container.

This costs no coverage: all 43 tests are about file format and none touch
the Contacts or EventKit readers. The integration those readers represent
remains verifiable only on a Mac.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01C5X1tYo9oxAfvoiFMh1QQr

README.md

@@ -92,6 +92,18 @@ swift test                       # run the test suite
 
 `Package.swift` opens directly in Xcode if you'd rather work there.
 
+### CI
+
+`.gitea/workflows/test.yml` runs `swift test` in a `swift:6.2` container on
+every push and pull request.
+
+It covers `IPodSyncKit` only. The Contacts and EventKit readers are compiled
+out on Linux via `#if canImport(…)`, and the SwiftUI app target is excluded
+from `Package.swift` on non-Apple platforms — neither can exist in a Linux
+container. No test coverage is lost by this: every test is about file format,
+and none of them touch the readers. What CI cannot tell you is whether reading
+from the real Contacts and Calendars databases still works; that needs a Mac.
+
 The bundle is **ad-hoc signed**, which is not the same as signed for
 distribution. Ad-hoc signing is required — Contacts and Calendars identify an
 app by its code signature, and an unsigned bundle gets denied or re-prompts