fix(app,packaging): keep libmpv and the taskbar icon across Windows upgrades

An MSI upgrade left the app without libmpv-2.dll until it was installed a
second time (B62). Costing runs before RemoveExistingProducts, saw the old
DLL at the same version and skipped the copy, and removing the old product
then deleted it. Both installer definitions now set REINSTALLMODE=amus;
every file is private to the install directory.

A taskbar pin lost its icon after a while (B63). The exe carried no icon
resource, and the Start Menu shortcut's icon lived in the per-ProductCode
installer cache that each upgrade deletes. build.rs now compiles the .ico
into proton-stream.exe, and the shortcut has no Icon of its own (and in the
WiX build is no longer advertised), so both show the exe's icon.

crates/pstr-app/Cargo.toml

@@ -34,6 +34,9 @@ directories.workspace = true
 chrono.workspace = true
 souvlaki.workspace = true
 
+[build-dependencies]
+embed-resource.workspace = true
+
 [dev-dependencies]
 skrifa.workspace = true
 

crates/pstr-app/build.rs

@@ -0,0 +1,15 @@
+//! Compiles `proton-stream.rc` into the Windows exe; nothing on any other
+//! target. `rc.exe` on an MSVC build, mingw's `windres` on the cross build
+//! from Linux.
+
+fn main() {
+    println!("cargo:rerun-if-changed=proton-stream.rc");
+    println!("cargo:rerun-if-changed=../../packaging/windows/proton-stream.ico");
+    if std::env::var("CARGO_CFG_TARGET_OS").as_deref() != Ok("windows") {
+        return;
+    }
+    // Only the GUI gets the icon; `pstr` is a console tool.
+    embed_resource::compile_for("proton-stream.rc", ["proton-stream"], embed_resource::NONE)
+        .manifest_optional()
+        .expect("compile the icon resource");
+}

crates/pstr-app/proton-stream.rc

@@ -0,0 +1,4 @@
+// The exe's icon. The window sets one at runtime too, but that only lasts as
+// long as the window: Explorer, the Start menu and a taskbar pin read the icon
+// out of the file, and without this one they fall back to the generic one.
+1 ICON "../../packaging/windows/proton-stream.ico"