Macos signing (#80)

* 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>

* Sign bundle contents serially

Signing the app image's Mach-O files with "xargs -P 8" passed locally but
failed on a runner: codesign reported "replacing existing signature" and then
"No such file or directory" for that same path. The two libjli.dylib copies are
separate inodes, so this is not hard links being signed twice -- concurrent
codesign runs over one bundle are simply not reliable. Serially costs about a
minute, since each call waits on Apple's timestamp server.

Also stop the matrix from cancelling the other architecture on a failure; that
throws away half the diagnostic information from a failed run.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Document macOS signing from 1.42

The installation guides described the right-click workaround as the normal
first launch. That stays, but as the path for 1.41.1 and older; from 1.42 a
double-click works. Both guides also show how to verify a download with spctl,
so the claim is checkable rather than something to take on faith.

The per-channel download notes distinguish where the channels actually stand:
Nightly is built from main and is signed as of now, while Stable still points
at 1.41.1, so those notes name the version instead of claiming it outright.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

github_docs/en-Installation.md

@@ -267,7 +267,19 @@ Apple Silicon Macs require the package marked `arm64`. Intel Macs require the pa
 3. Drag `KST4Contest.app` into the **Applications** folder.
 4. Start KST4Contest from the Applications folder or Launchpad.
 
-The application is not currently notarized by Apple. macOS may therefore block the first launch.
+From version 1.42 onwards the macOS packages are signed with an Apple Developer ID and notarized by Apple. The first launch therefore works by double-clicking, without going through the context menu and without a security prompt. The notarization ticket is stapled into the DMG file itself, so the check also succeeds without an internet connection.
+
+To confirm that a downloaded package really is signed, check it in a terminal:
+
+```bash
+spctl --assess --type open --context context:primary-signature -v KST4Contest-v<version>-macos-arm64.dmg
+```
+
+The expected result is `accepted` together with `source=Notarized Developer ID`.
+
+### Versions up to and including 1.41.1
+
+Older packages are not notarized, so macOS blocks the first launch.
 
 If the application came from the official GitHub Release:
 
@@ -408,7 +420,9 @@ Then start the file from a terminal. Error messages shown there are usually more
 
 ### macOS blocks the application
 
-Use the **Open** function described under [Installing on macOS](#installing-on-macos). Before doing so, verify that the DMG file came from the official GitHub Release.
+From version 1.42 onwards this should no longer happen, because the packages are signed and notarized. If it does occur, the DMG file was most likely downloaded incompletely or modified afterwards; download it again from the official GitHub Release.
+
+On older versions the block is expected. Use the **Open** function described under [Installing on macOS](#installing-on-macos).
 
 ### The problem remains