feat(windows): run numa as a real SCM service, drop Run-key autostart

Hooks the service-dispatcher scaffolding from the previous commit to
actually serve DNS, and replaces the HKLM\…\Run login-time autostart
with a proper Windows service created via sc.exe.

**Refactor**
- Extract main.rs's inline server body (~500 lines) into `numa::serve::run`
  so both the interactive CLI entry and the service dispatcher drive the
  same startup/serve loop. main.rs is now a thin subcommand router.
- main.rs goes sync (no #[tokio::main]); each branch that needs async
  builds its own runtime and block_on's. Required so the --service path
  can hand off to SCM without fighting tokio for the entry thread.

**Windows service wrapper**
- `numa::windows_service::run_service` now builds a multi-thread tokio
  runtime on a dedicated thread and runs `serve::run` inside it. Stop/
  Shutdown from SCM aborts the wait loop and reports SERVICE_STOPPED.
- Config path resolves to `%PROGRAMDATA%\numa\numa.toml` when running
  under SCM (SYSTEM's cwd is System32, relative paths don't work).

**Install/uninstall**
- `install_windows` now copies numa.exe to a stable
  `%PROGRAMDATA%\numa\bin\numa.exe` and registers it via `sc create`
  with start=auto, obj=LocalSystem, and a failure policy of
  restart/5000/restart/5000/restart/10000. Starts the service
  immediately when no reboot is pending.
- `uninstall_windows` stops + deletes the service and removes the
  binary copy before restoring DNS.
- Drops the old `register_autostart` / `remove_autostart` helpers that
  wrote to `HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run` — that
  path runs at user login in the user's session with no stderr capture
  and no crash-restart policy, which is why we've been flying blind in
  every Windows debug session.

DNS-set bugs (netsh destructive static, IPv6 not touched, uninstall
secondary-drop) and file logging are orthogonal — tracked for follow-up.

src/lib.rs

@@ -20,6 +20,7 @@ pub mod query_log;
 pub mod question;
 pub mod record;
 pub mod recursive;
+pub mod serve;
 pub mod service_store;
 pub mod setup_phone;
 pub mod srtt;