fix(deploy): relay + LNbits pubkey are seed-provided, not env-pinned (#70)

The bitspire-env activation seeded VITE_RELAY_URL from the relayUrl option
(default wss://relay.aiolabs.dev). Because env wins over the pairing seed, every
fresh machine pinned itself to that relay — which is dead — so a scanned seed's
relay was ignored ("No connected relays"; hit live on the aio-demo USB). Default
relayUrl to "" so both relay and server pubkey come from the seed; a non-empty
option now pins a machine (an explicit override) rather than being the default.
Descriptions updated to match.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

flake.nix

@@ -191,10 +191,11 @@
               # boots cleanly into the "needs provisioning" state; provision-
               # atm.sh SSHes in and overwrites with real values.
               #
-              # VITE_RELAY_URL seeds from `config.services.bitspire.relayUrl`
-              # so the NixOS module's `relayUrl` option becomes the default
-              # without losing the operator's ability to override via .env
-              # (edit the file or re-run provision-atm.sh).
+              # VITE_RELAY_URL + VITE_LNBITS_SERVER_PUBKEY seed EMPTY by default
+              # (relayUrl defaults to ""), so the pairing seed drives the relay
+              # + server pubkey (aiolabs/bitspire#70). A non-empty `relayUrl`
+              # option pins a machine to a specific relay (seeded here, wins over
+              # the seed via env-first precedence) — otherwise leave it blank.
               system.activationScripts.bitspire-env = ''
                 mkdir -p /var/lib/bitspire
                 if [ ! -f /var/lib/bitspire/.env ]; then