Update install failures become visible: blocked, aborted, failed (D-155)

The PackageInstaller session's final status now reaches UpdateRepository:
InstallResultReceiver hands it by session id to the waiting AndroidApkInstaller
call (ApkInstaller.install returns a PendingInstall). installOutcome() maps
STATUS_FAILURE_BLOCKED to UpdateFailure.Blocked, STATUS_FAILURE_ABORTED back to
Available without an error, and every other failure to UpdateFailure.Install
with the installer's EXTRA_STATUS_MESSAGE. The cached APK is deleted once the
installer answers, so "Try again" downloads again. UpdateBanner's Failed variant
shows the reason on S-4 and S-22; two core:design strings (en/sv) with their
docs/ux/strings.csv rows. Unit tests for the mapping, the repository outcomes
and the receiver; goldens: update_banner re-recorded, S-17-install-blocked,
S-17-install-failed and s22_about_install_blocked new.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TQd3pEP9UeN2uifbHknQ7B

android/core/model/src/main/kotlin/se/hagstedt/kvitt/model/Sync.kt

@@ -34,10 +34,28 @@ sealed interface UpdateState {
     data object None : UpdateState
     data class Available(val info: UpdateInfo) : UpdateState
     data class Downloading(val info: UpdateInfo, val progress: Float) : UpdateState
-    data class Failed(val info: UpdateInfo) : UpdateState
+
+    /** The download or the install failed (AC-16.4, D-155); [reason] picks the banner's text, "Försök igen" downloads again. */
+    data class Failed(val info: UpdateInfo, val reason: UpdateFailure = UpdateFailure.Download) : UpdateState
+
     data class NeedsInstallPermission(val info: UpdateInfo) : UpdateState
 }
 
+/** Why [UpdateState.Failed] (D-155). The downloaded file is deleted in every case. */
+sealed interface UpdateFailure {
+    /** No answer, an error, or the size or SHA-256 did not match (AC-16.4). */
+    data object Download : UpdateFailure
+
+    /** The installer refused the install as blocked (`STATUS_FAILURE_BLOCKED`): the phone's security settings. */
+    data object Blocked : UpdateFailure
+
+    /**
+     * Any other installer failure (invalid, conflict, storage, incompatible, timeout, generic). [detail] is the
+     * installer's own status message, null when it gave none; it names packages and error codes, never personal data.
+     */
+    data class Install(val detail: String?) : UpdateFailure
+}
+
 /** The outcome of [UpdateRepository.check] and [UpdateRepository.checkNow] (S-22, AC-16.6). */
 sealed interface UpdateCheck {
     /** No newer APK is published (or nothing is published); debug builds, which never check (AC-16.5), report this too. */