Update ATVM status reporting and credential handling docs

- change ATVM status formatting to the approved Markdown-table template with SUMMARY:, HOSTS:, TIMING:, and NOTES:
- document that normal status requests print locally only unless explicitly asked to send to Mattermost
- document Mattermost defaults and posting rules, including only sending after full run completion
- document the controller-side systemd watcher design for future automation
- add the secrets migration/cleanup review doc
- ignore .env.credentials.local in git and reflect the move toward using that local credentials file instead of hardcoded secrets

atvm/docs/automation/status-template.md

@@ -0,0 +1,62 @@
+# ATVM Status Template
+
+Use this as the default ATVM automation run-status template for:
+- local status responses in the terminal
+- Mattermost status posts after a completed run
+
+## Layout
+
+```md
+## ATVM Run Status
+### <build_name>
+
+**SUMMARY:**
+
+| Metric | Value |
+|---|---:|
+| finished | <n> |
+| passed | <n> |
+| failed | <n> |
+| skipped | <n> |
+
+**HOSTS:**
+
+| Host | Status | Detail |
+|---|---|---|
+| <host-name> | ✅ PASS | completed |
+| <host-name> | ⚠️ FAIL | <useful failure description> |
+| <host-name> | ⏳ RUN | in progress |
+| <host-name> | ⏭️ SKIP | <skip reason> |
+
+**TIMING:**
+
+| Metric | Value |
+|---|---|
+| start | <start time> |
+| end | <end time or n/a> |
+| total | <total or elapsed runtime> |
+| quickest | <host> - <runtime> or n/a |
+| longest | <host> - <runtime> or n/a |
+| average | <runtime> or n/a |
+
+**NOTES:**
+- <note>
+- <note>
+```
+
+## Rules
+- Keep `SUMMARY:`, `HOSTS:`, `TIMING:`, and `NOTES:` in that order.
+- Use the title format:
+  - `## ATVM Run Status`
+  - `### <build_name>`
+- Use Markdown tables for `SUMMARY:`, `HOSTS:`, and `TIMING:`.
+- Use one host per row in the `HOSTS:` section.
+- For completed hosts, prefer:
+  - `✅ PASS`
+  - `⚠️ FAIL`
+- For in-progress or skipped hosts, use:
+  - `⏳ RUN`
+  - `⏭️ SKIP`
+- Keep `Detail` concise.
+- Put broader context under `NOTES:`, not in the host table.
+- Use the same template for Mattermost and local operator-visible status output.