build(lite): enable Windows lite-backend cross-compile (.exe verified)

`build.sh --lite-backend --win-release` now cross-compiles a working
ObsidianDragonLite.exe with the real SDXL backend:

- Artifact platform follows the cross target: when only --win-release is
  requested, auto-select build/lite-backend/windows/ (previously always the host
  artifact, which would link a Linux .a into a Windows .exe).
- Link the Win32 system libs a Rust x86_64-pc-windows-gnu staticlib pulls in
  (rustls/schannel, ring, dirs, std) via DRAGONX_LITE_BACKEND_EXTRA_LIBS. The set
  is rustc's `--print native-static-libs` for the backend (winapi_* shims mapped
  to real mingw import libs); all 21 exist in mingw-w64.

Verified end to end on Linux:
- scripts/build-lite-backend-artifact.sh --platform windows cross-builds the
  backend to x86_64-pc-windows-gnu (~105 MB .a); rustls/ring cross-compile clean
  (no openssl blocker); all required litelib_* symbols present.
- build.sh --lite-backend --win-release -> release/windows/ObsidianDragonLite-
  <ver>.exe (PE32+ GUI x86-64, INCBIN-embedded, ~170 MB) + zip, with the same
  full-node-asset exclusion as Linux.

Not yet done: running the .exe on real Windows (cross-compiled only). Plan
updated.

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

build.sh

@@ -119,11 +119,15 @@ fi
 # scripts/build-lite-backend-artifact.sh. Auto-discovers build/lite-backend/<platform>/;
 # override the directory with DRAGONX_LITE_BACKEND_DIR.
 if $DO_LITE_BACKEND; then
+    # Artifact platform follows the cross target when exactly one non-host release is requested,
+    # so `--lite-backend --win-release` links the Windows backend (not the host's) automatically.
     case "$(uname -s)" in
         Linux)  lb_platform="linux" ;;
         Darwin) lb_platform="macos" ;;
         *)      lb_platform="linux" ;;
     esac
+    if $DO_WIN && ! $DO_LINUX && ! $DO_MAC; then lb_platform="windows"; fi
+    if $DO_MAC && ! $DO_LINUX && ! $DO_WIN; then lb_platform="macos"; fi
     lb_dir="${DRAGONX_LITE_BACKEND_DIR:-$SCRIPT_DIR/build/lite-backend/$lb_platform}"
     lb_lib=""
     for cand in "$lb_dir"/libsilentdragonxlite.a "$lb_dir"/libsilentdragonxlite.so "$lb_dir"/silentdragonxlite.lib; do
@@ -145,7 +149,13 @@ if $DO_LITE_BACKEND; then
         "-DDRAGONX_LITE_BACKEND_ABI=sdxl-c-v1"
     )
     [[ -f "$lb_manifest" ]] && CMAKE_LITE_ARGS+=("-DDRAGONX_LITE_BACKEND_MANIFEST=$lb_manifest")
-    info "Lite backend enabled: $lb_lib"
+    # A Rust x86_64-pc-windows-gnu staticlib pulls in Win32 system libs (rustls/schannel, ring,
+    # dirs, std) that the app doesn't already link. The set is rustc's `--print native-static-libs`
+    # for the backend (winapi_* shims mapped to the real mingw import libs); all exist in mingw-w64.
+    if [[ "$lb_platform" == "windows" ]]; then
+        CMAKE_LITE_ARGS+=("-DDRAGONX_LITE_BACKEND_EXTRA_LIBS=advapi32;ws2_32;kernel32;bcrypt;cfgmgr32;credui;crypt32;cryptnet;fwpuclnt;gdi32;msimg32;ncrypt;ntdll;ole32;opengl32;secur32;shell32;synchronization;user32;winspool;userenv")
+    fi
+    info "Lite backend enabled ($lb_platform): $lb_lib"
 fi
 
 should_bundle_full_node_assets() {