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/Cargo.lock

@@ -80,7 +80,7 @@ checksum = "a23eb6b1614318a8071c9b2521f36b424b2c83db5eb3a0fead4a6c0809af6e61"
 
 [[package]]
 name = "archipelago"
-version = "1.7.18-alpha"
+version = "1.7.19-alpha"
 dependencies = [
  "anyhow",
  "archipelago-container",