chore: bump version to 1.3.1 for OTA update testing

First release with working UI sidecar containers (--user 0:0, CHOWN caps)
and complete update pipeline (manifest publishing, archive extraction,
WebSocket notifications).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "archipelago"
-version = "1.3.0"
+version = "1.3.1"
 edition = "2021"
 description = "Archipelago Bitcoin Node OS - Native backend"
 authors = ["Archipelago Team"]