refactor(nwc): dedupe NWC tooling — use Sovran_Bitcoin's sovran-nwc

The Hub vendored a second copy of the NWC stack
(app/sovran_systemsos_web/nwc_hub_manager.py, nwc_audit.py,
nwc_lnurl_service.py, nwc_wallet_cli.py) and built its own nwc-wallet /
nwc-lnurl binaries from it. That copy drifted from the pinned Alby Hub
API contract (appId vs toAppId) and duplicated code that Sovran_Bitcoin
already ships and fixes.

Changes:
- Delete the four vendored modules; server.py now imports the canonical
  implementation directly (from sovran_nwc import nwc_hub_manager) from
  the sovran-nwc package (pkgs.sovran-bitcoin.nwc). API fixes in
  Sovran_Bitcoin now propagate to the Hub web app automatically.
- sovran-hub-web launcher: add <sovran-nwc>/lib/sovran-nwc to
  sys.path so the import resolves.
- Stop shipping nwc-wallet / nwc-lnurl binaries from sovran-hub-web:
  the flake already provides them (env-wrapped nwc-wallet with
  NWC_* vars via albyhub.nix, and nwc-lnurl.service via lnurl.nix).

Requires a Sovran_Bitcoin rev containing the toAppId fix (and the
LNURL module audit-log fix); bump the flake input afterwards:
  nix flake update sovran-bitcoin

Test:
  - nixos-rebuild switch
  - Hub Wallet Connections tab still lists/creates wallets
  - nwc-wallet list works from the operator shell
  - journalctl -u nwc-lnurl shows no import/contract errors

app/sovran_systemsos_web/server.py

@@ -39,7 +39,7 @@ from starlette.middleware.base import BaseHTTPMiddleware
 
 from .config import load_config, load_versions
 from . import systemctl as sysctl
-from . import nwc_hub_manager as _nwc_mgr
+from sovran_nwc import nwc_hub_manager as _nwc_mgr
 from . import support_ops as _support_ops
 from .security_helpers import (
     _nix_escape,