Add optimized multi-platform release CI/CD pipeline.

Split Windows builds into shared x64 prep and arch-specific packaging, add comprehensive caching, verification scripts, and a PR smoke workflow.

Co-authored-by: Cursor <cursoragent@cursor.com>

.github/actions/cache-cargo-windows/action.yml

@@ -0,0 +1,16 @@
+name: Cache Cargo (windows-setup)
+description: Cache registry, git sources, and target/ for the Windows installer Rust workspace
+
+runs:
+  using: composite
+  steps:
+    - name: Cache Cargo
+      uses: actions/cache@v4
+      with:
+        path: |
+          ~/.cargo/registry
+          ~/.cargo/git
+          app/desktop/windows-setup/target
+        key: cargo-windows-${{ runner.os }}-${{ hashFiles('app/desktop/windows-setup/Cargo.lock', 'app/desktop/windows-setup/**/*.rs') }}
+        restore-keys: |
+          cargo-windows-${{ runner.os }}-