fix(flatpak): prune microsoft/windows-rs git crates before vendoring

The flatpak CI was failing at "Downloading sources" with "No space left
on device": flatpak-cargo-generator walks the whole workspace Cargo.lock
and emits a `type: git` source for the windows-rs crates (windows +
windows-reactor + ~12 sub-crates, pinned by punktfunk-client-windows),
and flatpak-builder then FULL-clones that multi-GB repo — for a bundle
that only ever compiles `-p punktfunk-client-linux` and never touches a
windows-* crate.

New packaging/flatpak/prune-windows-lock.py writes a copy of Cargo.lock
with the windows-rs git packages stripped (matches on the `source =`
line, so a crate that merely lists a windows dependency is kept;
dependency-free so it also runs on the Deck's stock python). Both the CI
and build-flatpak.sh feed that pruned lock to the generator. The
committed Cargo.lock is untouched — cargo --offline only needs vendored
sources for the crates it actually builds, and the windows-rs crates are
not in the Linux client's dependency closure.

Verified locally: 14 crates pruned (507 -> 493 packages), zero windows-rs
`source =` lines remain, output parses as TOML, all Linux-client deps
(gtk4/ffmpeg-sys-next/sdl3/pipewire) intact.

This unblocks the flatpak build carrying the VAAPI green-screen fix
(a89b19a) for the Steam Deck.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/flatpak.yml

@@ -85,10 +85,17 @@ jobs:
         # flatpak builds with no network; vendor every crate from Cargo.lock into
         # cargo-sources.json next to the manifest (referenced by the manifest's
         # punktfunk-client module).
+        #
+        # Prune the microsoft/windows-rs git crates first: they belong to
+        # punktfunk-client-windows, which the flatpak never builds, and leaving them in makes
+        # flatpak-builder full-clone that multi-GB repo at build time → "No space left on
+        # device" (see packaging/flatpak/prune-windows-lock.py). The committed Cargo.lock is
+        # untouched; cargo --offline only needs sources for the crates it compiles.
         run: |
           curl -fsSL -o /tmp/flatpak-cargo-generator.py \
             https://raw.githubusercontent.com/flatpak/flatpak-builder-tools/master/cargo/flatpak-cargo-generator.py
-          python3 /tmp/flatpak-cargo-generator.py Cargo.lock \
+          python3 packaging/flatpak/prune-windows-lock.py Cargo.lock /tmp/Cargo.flatpak.lock
+          python3 /tmp/flatpak-cargo-generator.py /tmp/Cargo.flatpak.lock \
             -o packaging/flatpak/cargo-sources.json
 
       - name: Build the flatpak (install deps from Flathub, offline build)