feat(platform): add Reinstall helpers to Pacman and Yay

internal/platform/pacman.go

@@ -76,6 +76,17 @@ func (p Pacman) Install(ctx context.Context, pkgs []string) error {
 	return p.Runner.Run(ctx, "sudo", args...)
 }
 
+// Reinstall runs `sudo pacman -S --noconfirm <pkgs...>` WITHOUT `--needed`,
+// so pacman physically re-fetches and reinstalls the packages even if they
+// are already present. Used by the `--force` flag to bypass idempotency.
+func (p Pacman) Reinstall(ctx context.Context, pkgs []string) error {
+	if len(pkgs) == 0 {
+		return nil
+	}
+	args := append([]string{"pacman", "-S", "--noconfirm"}, pkgs...)
+	return p.Runner.Run(ctx, "sudo", args...)
+}
+
 // Update runs `sudo pacman -Syu --noconfirm` (full sync + system upgrade).
 // On Arch, a bare `pacman -Sy` followed by an install is the partial-upgrade
 // anti-pattern that can break the system when a dep's ABI changes, so we