chore: update flake.lock (nixpkgs, Sovran_Bitcoin 1.1.1, Bisq2 2.1.14) and integration

- Update flake.lock inputs:
  - sovran-bitcoin: b0da63b -> 50a8b76 (1.1.1 with RTL 0.15.13 and Nix-native sovran-nwc 2.0.0)
  - nixpkgs (nixos-unstable): c59305b -> fe13242 (Caddy 2.11.7, Tor 0.4.9.14, GNOME Remote Desktop 50.2, Bitcoin Core 31.1, Electrs 0.12.0, LND 0.21.4-beta, BTCPay Server 2.4.5, Matrix Synapse 1.162.0, LiveKit 1.13.8, Vaultwarden 1.37.4, Haven 1.2.2)
  - nixpkgs-stable (nixos-26.05): 78e9c78 -> 26f4107
  - btc-clients: 99b0442 -> 990d29e (Bisq 1.10.9, Bisq2 2.1.14, Sparrow 2.5.5)
  - nixvim: 5980a62 -> 453dc9c
- flake.nix: replace deprecated pkgs.system with pkgs.stdenv.hostPlatform.system for btc-clients packages
- modules/sovran-bitcoin-integration.nix: guard config.networking.domain against null/empty when both haven and nwc-wallets features are enabled
- app/sovran_systemsos_web/versions.json: sync static fallback service versions with updated flake inputs
- CHANGELOG.md: document updates under [Unreleased]

app/sovran_systemsos_web/versions.json

@@ -1,16 +1,16 @@
 {
-  "caddy.service": "2.8.4",
-  "tor.service": "0.4.8.12",
-  "gnome-remote-desktop.service": "46.0",
-  "bitcoind.service": "27.1.0",
-  "electrs.service": "0.10.6",
-  "lnd.service": "0.18.0",
-  "rtl.service": "0.15.12",
-  "btcpayserver.service": "2.4.2",
-  "albyhub.service": "1.24.0",
-  "mempool.service": "3.2.1",
-  "matrix-synapse.service": "1.115.0",
-  "livekit.service": "1.13.6",
-  "vaultwarden.service": "1.32.0",
-  "haven-relay.service": "0.1.0"
+  "caddy.service": "2.11.7",
+  "tor.service": "0.4.9.14",
+  "gnome-remote-desktop.service": "50.2",
+  "bitcoind.service": "31.1",
+  "electrs.service": "0.12.0",
+  "lnd.service": "0.21.4-beta",
+  "rtl.service": "0.15.13",
+  "btcpayserver.service": "2.4.5",
+  "albyhub.service": "2.0.0",
+  "mempool.service": "3.3.1",
+  "matrix-synapse.service": "1.162.0",
+  "livekit.service": "1.13.8",
+  "vaultwarden.service": "1.37.4",
+  "haven-relay.service": "1.2.2"
 }