Boot flipctl on the panel instead of the flipctl2 prototype

[Yury-MonZon]

Stacked on #168.

flipctl becomes what the image boots on the panel, in place of the flipctl2 prototype.

build-flipctl.sh builds it from flipctl-slint for arm64, natively on an arm64 builder and cross anywhere else, and stages the tree the ospack overlays onto /usr: /usr/bin/flipctl, its apps and remote-view assets under /usr/share/flipctl, and the unit the repository itself ships, so the image and a deploy from a checkout restart the same one. Nothing there links a C library (EGL and GBM are dlopened, wayland-client uses its Rust backend, slint renders in software), so a cross build needs only the aarch64 std and a linker.

slint 1.17.1 wants rustc 1.92 where trixie has 1.85, so the container and the documented prerequisites take cargo from trixie-backports with the arm64 std beside it, and the build stops with one line when either is missing rather than a hundred lines into the resolver.

sway is the only package added on flipctl's behalf, being the compositor it hosts apps in. What an app itself needs is left out: each manifest names its packages and flipctl offers to install them when that app is opened.

The prototype is unenabled rather than removed, so the Testing row can still hand the panel over: the two wants symlinks go, and cog-seat1 loses its [Install]. The other half of that, the node server's own [Install], is in flipperone-testing 02f67fd, which the ospack already stages from dev.

Verified on a Flipper One from a freshly flashed image: flipctl active on the panel and serving its remote view, cog-seat1 and fake-flipctl-node-server both loaded but not autostarted, and the Testing row able to hand the panel over.

Note for whoever builds this: the ospack step must actually rebuild, UPDATE_OSPACK=1 or a clean out/images/, or an existing debian-ospack.tar.zst is reused and none of this lands in the image.