Entrypoint steps are functions called from main (closes #163)

bin/entrypoint.sh was top-level code with one helper; the shell section
of the code style guide asks for every step in a function and a main
called at the end. The PORT and TRUSTED_PROXIES checks, the data
directory, starting each process, the wait loop, stopping both and the
exit are now functions, which main calls in order, setting the stop
trap before either process starts. It stays POSIX sh with no set -e.
Messages and exit codes are unchanged; the 8081 message is passed to
echo as two arguments so its line fits in 80 columns.

Model: opus-5-5

TODO.md

@@ -21,6 +21,13 @@ Run `make frontend-viewport-test` in CI as its own step; it is not part of
 
 # Completed Steps
 
+- 2026-10-19: `bin/entrypoint.sh` has each of its steps in a function, and a
+  `main` at the end calls them in order, as the shell section of the code style
+  guide asks ([#163](https://git.eeqj.de/sneak/netwatch/issues/163)). It is
+  still POSIX sh with no `set -e`, and does what it did, with the same messages
+  and exit codes. Checked by running the image with each script: a normal start,
+  bad `PORT`, `TRUSTED_PROXIES` and `DATA_DIR` values, `docker stop`, INT, and
+  nginx exiting on its own
 - 2026-10-19: while report files cannot be written, the health check answers 503
   with `"status":"error"` and the same fields, so the image's `HEALTHCHECK`
   reports the container `unhealthy`