Restart without reboot; retrievable logs incl. mpv exit reasons

Two related gaps on the headless kiosk: no way to restart the wall short
of a full reboot, and no way to see why a stream keeps flapping (the
daemon's stderr goes to sway on tty1, and mpv's stderr was discarded).

Restart in place:
- `rtsp-streamer restart` sends a control-socket command; the daemon
  tears down its mpv children and syscall.Exec's the on-disk binary.
  Same PID, same parent (sway), same env — keeps WAYLAND_DISPLAY/
  SWAYSOCK and comes back up on the new binary, no reboot. Handles the
  os.Executable() "(deleted)" sentinel from make install's rename.
- sway config now launches the daemon in a relaunch loop, so a crash (or
  the restart) auto-recovers instead of leaving a black screen.
- `make deploy` now does `install` + `restart` instead of restarting
  getty@tty1 (which left stale duplicate sessions and forced reboots).

Retrievable logs:
- New internal/logbuf ring; the daemon tees slog output into it and
  serves the tail over the socket via `rtsp-streamer logs [-n N]` —
  readable over SSH, no file wrangling, no reboot.
- Capture the tail of each mpv's stderr and log its last line when the
  process exits, so "mpv exited, will restart" now carries the reason
  (connection refused, unsupported codec, 401, ...). This is the
  diagnostic for a single tile going unhealthy repeatedly.

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

README.md

@@ -144,6 +144,9 @@ rtsp-streamer status             # slot health from the running daemon
 rtsp-streamer layout ls          # list layouts (* marks active)
 rtsp-streamer layout set quad    # switch live (persists the choice)
 rtsp-streamer reload             # apply hand-edits to the config live
+rtsp-streamer restart            # re-exec the daemon in place (picks up a new
+                                 #   binary; no reboot)
+rtsp-streamer logs -n 80         # recent daemon activity incl. mpv exit reasons
 rtsp-streamer version            # baked-in git commit / build date
 ```
 
@@ -207,14 +210,21 @@ Then `sudo reboot` and the wall comes up on boot.
 ### Updating
 
 ```sh
-git pull && make install && sudo reboot
+git pull && make deploy
 ```
 
-`make install` builds natively and copies to `/usr/local/bin` (auto-sudo — run
-it *without* `sudo` so `go build` keeps your `PATH`). Use **`sudo reboot`**, not
-`systemctl restart getty@tty1`: a getty restart tends to leave the old sway +
-daemon running alongside the new one (duplicate mpv, windows fighting). Confirm
-what's live with `rtsp-streamer version`.
+`make deploy` builds natively, copies to `/usr/local/bin` (auto-sudo — run it
+*without* `sudo` so `go build` keeps your `PATH`), then runs
+`rtsp-streamer restart`, which tells the running daemon to **re-exec itself in
+place**: same process, same sway session, now running the new binary — no
+reboot, no duplicate sessions. Confirm what's live with `rtsp-streamer version`.
+
+`restart` works because the daemon is launched under a small relaunch loop in
+the sway config, so it also recovers on its own if it ever crashes. (Older
+installs that predate this launcher need their sway config refreshed — re-run
+`deploy/install.sh` or copy `deploy/sway/config` to
+`/etc/rtsp-streamer/sway/config` once, then reboot.) A full `sudo reboot` is
+still fine and never wrong.
 
 ## Enabling RTSP in UniFi Protect
 
@@ -262,6 +272,12 @@ pegged, work through:
 
 ## Troubleshooting
 
+- **A stream keeps going unhealthy / flapping** — `rtsp-streamer logs` shows the
+  daemon's recent activity, including the *reason* each mpv exited (its stderr
+  tail: connection refused, unsupported codec, 401, etc.). This is the first
+  thing to check when one tile restarts repeatedly. A camera whose `video-codec`
+  is `hevc` can't hardware-decode on a Pi 4 and often stutters/exits under load —
+  switch it to H.264 in Protect or give the tile the `low` substream.
 - **`status` can't reach the daemon** (`control.sock: no such file`) — the wall
   is running as a *different user* than your SSH session (check
   `ps -o user= -p "$(pgrep -x sway)"` vs `id`). Re-run `install.sh <your-user>`
@@ -306,7 +322,7 @@ pegged, work through:
 ## Layout
 
 ```
-cmd/rtsp-streamer/   CLI (cobra): daemon, discover, layout, reload, status, tui, config, version
+cmd/rtsp-streamer/   CLI (cobra): daemon, discover, layout, reload, restart, logs, status, tui, config, version
 internal/config/     YAML load/save/validate, schema (tiles, streams), XDG paths
 internal/protect/    UniFi Protect client (login, bootstrap, enable RTSP, URLs)
 internal/player/     one supervised mpv per stream, JSON IPC, restart/backoff