- update the watcher to detect the active categorized sub-run from the live `--ci-build-id` process state instead of treating the parent run as one synthetic grouped run
- fix host XML parsing so the watcher prefers the real host suite over the `Root Suite` entry, avoiding `0 tests, 0 failures` summaries
- use the first timestamp inside the run log as the watcher start time so restarted watchers do not miss current-run categorized artifacts because of log file mtime drift
- improve active-host inference for categorized runs so the watcher maps the current categorized build to the correct host family while the sub-run is still in progress
- update the watcher design and automation guide to treat --categorize as sequential ATVM sub-runs rather than one parent run with internal phases
- document that categorized runs should send one Mattermost status per completed grouped sub-run instead of one parent-only final post
- add a --categorize option to the watcher start helper so categorized mode is explicit in watcher startup
- update the watcher implementation to track categorized sub-runs separately, write per-subrun state, and post each completed grouped run once
- add the per-run ATVM watcher service package under atvm/watcher-service, including the Python watcher, systemd template unit, helper scripts, and deployment docs
- document the watcher-service install and operating model, including one-run-per-instance behavior, Mattermost posting rules, and the best-practice /opt/atvm-watcher-service install path
- clarify ATVM run approval semantics so `approve` means run without watcher and `approve with watcher` means run and start the watcher
- update the ATVM automation guide and AGENTS rules so watcher usage and approval behavior are explicit and consistent
