enh(logging): add a log_to_file setting so motion can log to stdout

[JamBalaya56562]

Summary

• add a log_to_file setting to settings.py and motioneye.conf.sample, overridable by the existing -l CLI flag
• have motionctl honour it: when file logging is off, motion inherits motionEye's own stdout/stderr instead of being redirected to <log_path>/motion.log

Fixes #3330. Implements @MichaIng's outline from #3330 (comment).

Why

motion's output was redirected to <log_path>/motion.log unconditionally, so containerized setups could not see it through docker logs at all. motionEye's own log already goes to stderr by default — only motion's was diverted to a file.

How

• settings.py / motioneye.conf.sample — new log_to_file setting. The log_path note is on the log_to_file entry, since that is where a reader lands.
• meyectl.py — -l is now resolved in load_settings() next to -d, i.e. after the config file is parsed, so the CLI wins. That makes settings.LOG_TO_FILE the single source of truth, and the five configure_logging() call sites no longer need to pass the flag (shell.py needs no new import).
• server.py — -b still forces file logging, because daemonizing redirects stdout/stderr to /dev/null (Daemon.daemonize()); without this, motion's output would be lost.
• motionctl.py — _get_motion_log_file() returns None when file logging is off, which makes Popen hand motionEye's own stdout/stderr to motion.
• handlers/log.py — /log/motion/ now returns 404 instead of an unhandled FileNotFoundError, since a missing motion.log is the default state after this change.

Default is false — rationale

how it's started	args	today
extra/motioneye.systemd	startserver -c …	no -l/-b → motionEye logs to stderr, only motion goes to a file
docker/entrypoint.sh	startserver -c …	same — this is exactly what #3330 is about
extra/motioneye.sysv	startserver -c … -l -b	explicitly opts into file logging

So false leaves motionEye's own logging untouched and merely makes motion consistent with it, while sysv users are unaffected. A true default would instead push every systemd user's motionEye log out of journald and into a file, which is the more disruptive change.

Behaviour changes to be aware of

1. motion.log is no longer written by default. systemd/Docker users get motion's output in journald / docker logs; set log_to_file true to restore the file.
2. -l can only enable file logging, not disable it (log_to_file true in the config cannot be overridden back to false on the command line). This mirrors how -d relates to log_level, so I kept it consistent — happy to add a --no-log-to-file if you'd prefer it to be symmetric.
3. Drive-by: removed two leftover sys.stderr.write debug lines in configure_logging() that printed on every single invocation. They're squarely in the way of this PR's goal (clean stdout), but say the word and I'll split them out.

Deliberately out of scope

• Reducing motion's log level ("I guess we'd need to reduce the motion log level as well") — separate concern, keeping this PR minimal.
• The pre-existing fd leak in motionctl.start() (log_file is never closed).
• server.py exiting fatally when LOG_PATH isn't writable — arguably more wrong now that the directory can go unused, but pre-existing.

Validation

• pytest tests/ → 141 passed (139 before + the new ones); ruff check, ruff format --check, flake8, isort, codespell all clean with the repo's pre-commit args.
• New tests: tests/test_meyectl.py (config parses log_to_file as a bool, -l overrides it), tests/test_motionctl.py (_get_motion_log_file() returns None vs. an open motion.log), tests/test_handlers/test_log.py (404 when absent, still served when present).
• E2E against a live server with motion 4.5.1 and a camera configured:

scenario	result
default (log_to_file unset)	[0:motion] [NTC] … lines appear on motionEye's stdout; no motion.log created ✅
log_to_file true	motion.log + motioneye.log written, stdout quiet ✅
-l with log_to_file false	both files written — CLI override works ✅
-b with log_to_file false	motion.log still written — output not lost to /dev/null ✅
GET /log/motion/ with log_to_file false	404, not a 500 traceback ✅