build: bump freedesktop runtime 24.08 -> 25.08

24.08 ships libpipewire/gst-plugin-pipewire 1.2.4, whose buffer negotiation
fails against KWin 6.7 + PipeWire 1.6.9 hosts (pipewiresrc: error alloc
buffers). 25.08 (libpipewire 1.4.9) was verified working on openSUSE Kalpa
via flatpak run --runtime-version=25.08; the host only needs the PipeWire
daemon, so older hosts (Mint 22, PipeWire 1.0) stay compatible.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

scripts/make-flatpak.sh

@@ -16,7 +16,7 @@ set -euo pipefail
 cd "$(dirname "$0")/.."
 
 APP_ID=de.pc_heini.HeiniRemoteAgent
-RUNTIME_VER=24.08
+RUNTIME_VER=25.08
 BRANCH=stable
 AGENT_BIN="${AGENT_BIN:?set AGENT_BIN to the compiled heiniremote-agent}"
 WL_DIR="${WL_CLIPBOARD_DIR:-/usr/bin}"