fix(thumbnailer-win): make the COM DLL compile on the MSVC target

First real Windows build surfaced errors that a Linux host couldn't catch:

* Enable the missing `windows` feature gates (Win32_System_LibraryLoader,
  Win32_System_SystemServices, Win32_Security — the last brings in the
  `Ex` registry APIs) so the imports resolve.
* Depend on `windows-core`: the `#[implement]` macro expands to
  `windows_core::` paths, which need the crate nameable in the root.
* `IClassFactory::LockServer` takes `Win32::Foundation::BOOL`, not a
  `core` BOOL.
* Name the returned image type via a new `dwg_thumbnailer::RgbaImage`
  re-export instead of a direct `image` dependency.

Verified with `cargo check --target x86_64-pc-windows-gnu -p
dwg-thumbnailer-win` (and the native check still passes).

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

crates/dwg-thumbnailer/src/lib.rs

@@ -11,7 +11,10 @@
 
 use std::path::Path;
 
-use image::{ImageFormat, RgbaImage};
+use image::ImageFormat;
+// Re-exported so downstream crates (the Windows/macOS handlers) can name the
+// returned image type without taking their own direct `image` dependency.
+pub use image::RgbaImage;
 
 /// Read the DWG at `path`, extract its embedded preview, and scale it so the
 /// longest edge is at most `max_dim` pixels (aspect preserved). Returns `None`