fix(windows): embed the app icon into the .exe

The Windows executable carried no icon, so Explorer, the taskbar, the
Start-menu tile and file-association entries showed a generic icon. Embed
AppIcon.ico via winresource in build.rs, and generate the .ico from the logo
before the build (it was produced after the build, too late to embed). Local
and non-Windows builds skip the step when the .ico is absent.

Fixes #107.

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

.github/workflows/release.yml

@@ -75,6 +75,18 @@ jobs:
       - name: Install Rust
         uses: dtolnay/rust-toolchain@stable
 
+      - name: Convert SVG icon to ICO
+        shell: pwsh
+        run: |
+          # ImageMagick is pre-installed on windows-latest. The
+          # auto-resize generates every size Explorer / Add-Remove
+          # Programs / the Start Menu shortcut may request from a
+          # single source SVG. Must run BEFORE the build so build.rs
+          # can embed the icon into the .exe (issue #107).
+          magick assets/logo.svg `
+            -define icon:auto-resize=16,24,32,48,64,128,256 `
+            packaging/windows/AppIcon.ico
+
       - name: Build
         run: cargo build --release
 
@@ -96,17 +108,6 @@ jobs:
           timestamp-rfc3161: http://timestamp.acs.microsoft.com
           timestamp-digest: SHA256
 
-      - name: Convert SVG icon to ICO
-        shell: pwsh
-        run: |
-          # ImageMagick is pre-installed on windows-latest. The
-          # auto-resize generates every size Explorer / Add-Remove
-          # Programs / the Start Menu shortcut may request from a
-          # single source SVG.
-          magick assets/logo.svg `
-            -define icon:auto-resize=16,24,32,48,64,128,256 `
-            packaging/windows/AppIcon.ico
-
       - name: Build MSI installer
         shell: pwsh
         run: |