Sign and notarize macOS builds

jpackage cannot produce a distributable macOS bundle on its own. It ad-hoc
signs the embedded runtime and then re-runs codesign on the same files without
--force, which codesign rejects; and "--type dmg --app-image" re-signs the app
it is handed, replacing a Developer ID signature with an ad-hoc one. So the
build now creates an unsigned app-image, signs it from the inside out, and
wraps it with hdiutil.

Apple's notary service also unpacks JARs and checks the native libraries
inside them, which sqlite-jdbc ships for both architectures. Those are signed
before the bundle is sealed, since rewriting a JAR afterwards would invalidate
the seal. A preflight check verifies Apple's two criteria locally, so a missed
binary costs seconds rather than a round trip to the notary service.

Two long-standing defects surfaced while testing and are fixed here: the
bundle identifier defaulted to the main class's package name (kst4contest.view
instead of de.x08.KST4Contest), and every release reported version 1.0 in
Finder because --app-version was never passed. Neither affects existing users:
the app keeps its settings in ~/.praktiKST, independent of the bundle ID.

Both workflows call the same script the local Mac uses, so the two cannot
drift apart. Signing needs a keychain that can answer a UI prompt, which a
runner cannot, so ci-import-cert.sh creates a throwaway keychain whose
password is generated per job and discarded with it. Notarization goes through
an App Store Connect API key and needs no keychain at all.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WYcmHra3YndA1ahkHeNdJ2

.gitignore

@@ -44,3 +44,6 @@ website/_site/
 
 # Local secrets for act testing
 .secrets
+
+# Apple notarization private keys - never commit these
+*.p8