desktop: generate the Windows icon set in the cross-compile job

tauri-build needs icons/icon.ico to emit the Windows Resource file, and the
repo only carries the PNG set the Linux bundles use — run 2881 failed with
"icons/icon.ico not found".

Generated in-job from the committed 1024px app-icon.png rather than committing
a hand-made .ico, so there stays one icon of record that can't silently drift
from the brand art. Scoped to the windows job; the Linux bundles don't need it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SreJkbxB4gx8pPsu8QbLPi

.forgejo/workflows/desktop.yml

@@ -155,6 +155,15 @@ jobs:
         run: npm ci && npm run build
         working-directory: frontend
 
+      # tauri-build generates a Windows Resource file and needs `icons/icon.ico`,
+      # which the repo doesn't carry — only the PNG set the Linux bundles use.
+      # Generating it from the committed 1024px source keeps one icon of record
+      # instead of a hand-made .ico that could silently drift from the brand art.
+      # Linux doesn't need this step, which is why it lives here and not in `build`.
+      - name: Generate the Windows icon set
+        run: cargo tauri icon app-icon.png
+        working-directory: desktop/src-tauri
+
       # --runner cargo-xwin swaps cargo for the cross-compiling driver (it supplies
       # the MSVC CRT/SDK, pre-warmed into the image, and links with lld-link).
       # Frontend already built above; skip the beforeBuildCommand rebuild.