refactor(host/windows): clean up DDA path + add a proper Windows service

Final cleanup after the DDA-parity work, plus an end-user service to replace the
PsExec/VBS/scheduled-task launch chain.

Cleanup (behavior-preserving):
- sudovda.rs: drop the dead legacy GDI isolate_displays/restore_displays (CCD is
  the sole isolation path), the always-empty Monitor.isolated field, and the
  vestigial reassert_isolation + PUNKTFUNK_ISOLATE_DISPLAYS knob; fix stale comments.
- dxgi.rs: downgrade leftover debug warns/infos (DuplicateOutput1 retry, FALLBACKS,
  hook-hits, AcquireNextFrame idle timeout) to debug!; remove the PUNKTFUNK_NO_CURSOR
  per-frame test knob.

Windows service (src/service.rs, `punktfunk-host service`):
- SCM supervisor (windows-service crate) that duplicates its LocalSystem token,
  retargets it to the active console session, and CreateProcessAsUserW's the host
  there (Sunshine/Apollo model) — relaunching on exit and console session switch,
  inside a kill-on-close job object so a service crash never orphans the host.
- install/uninstall/start/stop/status subcommands: one elevated `service install`
  registers an auto-start LocalSystem service + firewall rules + a default host.env.
- Config moves to %ProgramData%\punktfunk\host.env; config_dir() now resolves to
  %ProgramData%\punktfunk on Windows (replacing the APPDATA=C:\Users\Public hack),
  with a PUNKTFUNK_CONFIG_DIR override. Logs land in %ProgramData%\punktfunk\logs\.
- merged_env_block (shared with the WGC helper) now also carries RUST_LOG.
- docs/windows-service.md + scripts/windows/host.env.example; windows-host.md updated.

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

Cargo.lock

@@ -2688,6 +2688,7 @@ dependencies = [
  "wayland-protocols-wlr",
  "wayland-scanner",
  "windows 0.62.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "windows-service",
  "x509-parser",
  "xkbcommon",
 ]
@@ -4325,6 +4326,12 @@ dependencies = [
  "safe_arch",
 ]
 
+[[package]]
+name = "widestring"
+version = "1.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72069c3113ab32ab29e5584db3c6ec55d416895e60715417b5b883a357c3e471"
+
 [[package]]
 name = "winapi"
 version = "0.3.9"
@@ -4557,6 +4564,17 @@ dependencies = [
  "windows-link 0.2.1 (git+https://github.com/microsoft/windows-rs?rev=b4129fcc1ae81eec8bf1217539883db821bca3a1)",
 ]
 
+[[package]]
+name = "windows-service"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d24d6bcc7f734a4091ecf8d7a64c5f7d7066f45585c1861eba06449909609c8a"
+dependencies = [
+ "bitflags",
+ "widestring",
+ "windows-sys 0.52.0",
+]
+
 [[package]]
 name = "windows-strings"
 version = "0.5.1"