Replace the greetd gamescope-session (which required STROM_NO_GAMESCOPE and
rendered games directly in the session compositor) with greetd launching sway.

A game's nested gamescope prefers its wayland backend, which needs wlroots
protocols that cage (and, differently, an outer gamescope session) do not give
it. Under those it fell back to gamescope's SDL backend, whose Vulkan swapchain
remake loops and aborts on this RADV RENOIR iGPU (rendervulkan.cpp
vulkan_remake_swapchain) - crashing e.g. Baba Is You a couple seconds in. sway
exposes those protocols, so gamescope inits its wayland backend and never hits
the crashing SDL path. Every game keeps its own gamescope (render resolution,
in-game exit chord, bare-tty portability); no per-game workaround needed.

Also resolve STROM_FLAKE to the /home/strom/strom checkout when present (github
fallback) so changes can be tested on the box before pushing upstream.

Xbox pads pair via JustWorks; on reconnect a pad whose bond went stale
re-initiates pairing, which needs a registered agent to auto-confirm. bluetuith
only has an agent while actively pairing in it, so an autonomous re-pair hit
"No agent available for request type 2" and the link dropped right after
connecting. Run bt-agent -c NoInputNoOutput as a persistent default agent so
pairing/re-pairing always completes.

Also set TemporaryTimeout=30 so the LAN party's hundreds of stray BLE devices
are evicted from the cache instead of piling up and saturating the adapter.