release(v1.7.19-alpha): kill stale available_update + numeric version compare

load_state now drops any stored available_update whenever the running
binary version differs from what's on disk — the old migration only
cleared it when the stale entry happened to match the new version, so
skipping releases (e.g. sideloading 1.7.16 → 1.7.18 without 1.7.17)
left a pointer to an intermediate version as the "update available",
which the UI then offered as a downgrade prompt.

check_for_updates also uses a numeric version comparator so a stale or
cached manifest with an older version can't offer itself as an
update, and 1.7.10 correctly outranks 1.7.9 past the single-digit
patch boundary.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

core/archipelago/src/federation/invites.rs

@@ -342,6 +342,7 @@ mod tests {
             "local.onion",
             "localpub",
             None,
+            None,
             |_| "test-sig".to_string(),
         )
         .await
@@ -376,6 +377,7 @@ mod tests {
             "local.onion",
             "localpub",
             None,
+            None,
             |_| "test-sig".to_string(),
         )
         .await
@@ -409,6 +411,7 @@ mod tests {
             "local.onion",
             "localpub",
             None,
+            None,
             |_| "test-sig".to_string(),
         )
         .await
@@ -421,6 +424,7 @@ mod tests {
             "local.onion",
             "localpub",
             None,
+            None,
             |_| "test-sig".to_string(),
         )
         .await