feat: sidebar update card (web + macOS) with app-first mac update flow and Sparkle beta track (#104171)

* feat: sidebar update card (web + macOS) with app-first mac update flow and Sparkle beta track

Squashed from claude/update-notification-display-c6cfb9 after semantic merge
with #104178 (channel-aware CLI installs). See PR #104171 body for details.

* chore(i18n): resync generated inventories after rebase

* chore(i18n): resync locale metadata after rebase

scripts/make_appcast.sh

@@ -38,6 +38,15 @@ if [[ -z "$VERSION" ]]; then
   fi
 fi
 
+CHANNEL_ARGS=()
+if [[ "$VERSION" == *-alpha.* || "$VERSION" == *.alpha.* ]]; then
+  echo "Alpha releases do not ship via Sparkle: $VERSION" >&2
+  exit 1
+fi
+if [[ "$VERSION" == *-beta.* || "$VERSION" == *.beta.* ]]; then
+  CHANNEL_ARGS=(--channel beta)
+fi
+
 TMP_DIR="$(mktemp -d)"
 NOTES_HTML=""
 cleanup() {
@@ -74,6 +83,7 @@ fi
   --download-url-prefix "$DOWNLOAD_URL_PREFIX" \
   --embed-release-notes \
   --link "$FEED_URL" \
+  "${CHANNEL_ARGS[@]}" \
   "$TMP_DIR"
 
 cp -f "$TMP_DIR/appcast.xml" "$ROOT/appcast.xml"

scripts/release-check.ts

@@ -1107,6 +1107,7 @@ export function collectAppcastSparkleVersionErrors(xml: string): string[] {
     const title = extractTag(item, "title") ?? "unknown";
     const shortVersion = extractTag(item, "sparkle:shortVersionString");
     const sparkleVersion = extractTag(item, "sparkle:version");
+    const sparkleChannel = extractTag(item, "sparkle:channel");
 
     if (!sparkleVersion) {
       errors.push(`appcast item '${title}' is missing sparkle:version.`);
@@ -1120,6 +1121,9 @@ export function collectAppcastSparkleVersionErrors(xml: string): string[] {
     if (!shortVersion) {
       continue;
     }
+    if (/(?:^|[.-])beta(?:[.-]|$)/i.test(shortVersion) && sparkleChannel !== "beta") {
+      errors.push(`appcast item '${title}' must set sparkle:channel to 'beta'.`);
+    }
     const floors = sparkleBuildFloorsFromShortVersion(shortVersion);
     if (floors === null) {
       errors.push(