packaging: the rolling-release prune was eating the Android client

Run 4092 published `thoughtsync.apk` to the `dev` release. Run 4098 removed it,
four minutes later, and both runs were green.

`write-manifest.sh` prunes the rolling channel to stop ~100 MB AppImages
accumulating forever, keeping `latest.json` and anything whose name contains the
current `$APP_VERSION`. The Android assets deliberately have no version in their
names — a fixed name is the only addressable URL on a tag that never moves,
which is the entire reason the `dev` release exists — so they matched neither
rule and were swept.

They would have been swept even if they HAD carried a version: Android is a
different workflow with its own run number, so its version never equals the
desktop's `$APP_VERSION` in this script.

The keep-list is now about fixed names rather than about `latest.json`
specifically, which is what the rule always meant. A fixed-name asset is
self-limiting — each publish replaces the same name — so the accumulation this
prune exists to prevent cannot happen to one.

Worth noting how this presented: two green runs and a missing file. Nothing
failed, and the only way to see it was to ask the release what it actually held
rather than trusting that a step named "Publish" had published.

desktop/packaging/write-manifest.sh

@@ -168,9 +168,21 @@ if [ "${PRUNE_OLD_ASSETS:-false}" = "true" ]; then
     | while IFS= read -r row; do
         asset_id="$(printf '%s' "$row" | grep -oE '[0-9]+' | head -1)"
         asset_name="$(printf '%s' "$row" | sed -E 's/.*"name"[[:space:]]*:[[:space:]]*"([^"]+)".*/\1/')"
-        # Keep the manifest itself and everything belonging to the current build.
+        # Keep FIXED-NAME assets and everything belonging to the current build.
+        #
+        # A fixed name is self-limiting: each publish replaces that same name, so
+        # it cannot accumulate and the reason this prune exists does not apply to
+        # it. It is also the only kind of URL that stays addressable on a rolling
+        # tag, which is the whole point of having one — deleting it breaks
+        # whatever was pointing at it.
+        #
+        # The Android client is on that list for a second reason too: it is built
+        # by a DIFFERENT workflow with its own run number, so its version never
+        # matches $APP_VERSION here and a version-stamped name would be pruned on
+        # every desktop push regardless. That is exactly what happened on run
+        # 4098, which swept the APK run 4092 had just published.
         case "$asset_name" in
-          latest.json) continue ;;
+          latest.json|thoughtsync.apk|thoughtsync-android.json) continue ;;
           *"$APP_VERSION"*) continue ;;
         esac
         echo "    removing $asset_name"