session logging, build-only mode, park splash, boot logo spinner

- Per-process stderr logging to /data/log2/{session}/ with time-safe
  directory naming (boot-xxx renamed once GPS/NTP sets clock)
- Aggregate session.log with major events (start/stop, transitions)
- 30-day log rotation cleanup on manager startup
- build_only.sh: compile without starting manager, non-blocking error
  display, kills stale processes
- build.py: copies updated spinner binary after successful build
- Onroad park mode: show splash screen when car is on but in park,
  switch to camera view when shifted to drive, honor screen on/off
- Spinner: full-screen boot logo background from /usr/comma/bg.jpg
  with white progress bar overlay
- Boot logo: auto-regenerate when boot_logo.png changes, 140% scale
- launch_openpilot.sh: cd to /data/openpilot for reliable execution
- launch_chffrplus.sh: kill stale text error displays on startup
- spinner shell wrapper: prefer freshly built _spinner over prebuilt

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

launch_chffrplus.sh

@@ -79,6 +79,9 @@ function launch {
     agnos_init
   fi
 
+  # CLEARPILOT: kill stale error display from previous build/run
+  pkill -f "selfdrive/ui/text" 2>/dev/null
+
   # write tmux scrollback to a file
   tmux capture-pane -pq -S-1000 > /tmp/launch_log