fetch_all_channels() connects to each daemon socket and calls
list() via capnp RPC. Runs on a dedicated thread (capnp uses Rc).
Results sent back via mpsc channel, TUI reads cached state.
Fetched at startup and when switching to F5 thalamus screen.
Also calls ensure_running() to restart dead daemons.
Co-Developed-By: Kent Overstreet <kent.overstreet@linux.dev>