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>

.gitea/workflows/build-flatpak.yml

@@ -30,10 +30,13 @@ jobs:
   build:
     runs-on: ubuntu-latest
     container:
-      # ubuntu:24.04 matches the freedesktop 24.08 runtime closely enough
-      # (glibc 2.39, GStreamer 1.24) that the cargo-built binary runs
-      # unmodified inside the runtime. Privileged so Flatpak's bwrap works
-      # where needed (runtime install triggers).
+      # ubuntu:24.04 (glibc 2.39, GStreamer 1.24) is older than the
+      # freedesktop 25.08 runtime (glibc 2.41, GStreamer 1.26), so the
+      # cargo-built binary runs unmodified inside the runtime (same sonames,
+      # forward-compatible symbol versions). 25.08 is required: 24.08 ships
+      # libpipewire 1.2 whose buffer negotiation fails against KWin 6.7 /
+      # PipeWire 1.6 hosts ("pipewiresrc: error alloc buffers"). Privileged
+      # so Flatpak's bwrap works where needed (runtime install triggers).
       image: ubuntu:24.04
       options: --privileged
     steps:
@@ -120,7 +123,7 @@ jobs:
         if: steps.check.outputs.build == 'true'
         run: |
           flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
-          flatpak install -y flathub org.freedesktop.Platform//24.08 org.freedesktop.Sdk//24.08
+          flatpak install -y flathub org.freedesktop.Platform//25.08 org.freedesktop.Sdk//25.08
 
       - name: Stamp version into AppStream metadata
         if: steps.check.outputs.build == 'true'