Mac mini support: arm64 cross-build installed beside the binary and pushed by arch; ARM machine name from the device tree

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

PLAN.md

@@ -200,7 +200,10 @@ something long in one, switch away and back, refresh — it's all still there.
   it last, so one deploy on the hub updates every machine. First install on a new host
   is still by hand (scp binary + `install.sh`, `hamlab passwd`, `tls auto`). Still to
   do: Phase 2 Datacenter overview; optional firewall rule limiting a node's port to
-  the hub; cross-architecture builds for the Mac mini.
+  the hub. **Cross-architecture** (2026-09-18): `make deploy` also builds
+  `bin/hamlab-linux-arm64`, `install.sh` installs it beside the binary as
+  `hamlab-arm64`, and the hub picks the sibling matching a node's `/api/me.arch` when
+  pushing — the Mac mini (Fedora Asahi, aarch64, node `mac`) updates like the rest.
 - **Auth hardening** — WebAuthn passkeys (phone Face ID), TOTP fallback, session
   list + revoke, optional NPM access list restricting to WireGuard/LAN.
 - **Files tab** — **shipped 2026-09-18** (`internal/files`, `Files.tsx`): browse from