claude-plugins: scope the swarm-logs example by machine id

The worked example keyed a stream selector on `_HOSTNAME`, which the
collector config warns against: a hostname is a config value two
machines can share, so keying on it merges their streams. Use
`_MACHINE_ID`, which is the field that actually distinguishes them.

Refs #4460

report.md

@@ -0,0 +1,43 @@
+# Report — #4460 swarm-logs skill
+
+PR: https://forge.constellation.darkest.space/hyperhive/hyperhive/pulls/4471
+
+## git show --stat
+```
+b9e62b06 claude-plugins: add a swarm-logs skill
+ 1 file changed, 84 insertions(+)
+ create mode 100644 claude-plugins/plugins/base/skills/swarm-logs/SKILL.md
+```
+
+## Verbatim `--help` checked flags against
+```
+$ swarm-logs --help
+query the swarm's log store from an agent
+Usage: swarm-logs <COMMAND>
+Commands: query, help
+Options: -h/--help, -V/--version
+
+$ swarm-logs query --help
+Usage: swarm-logs query [OPTIONS] <LOGSQL>
+Arguments: <LOGSQL> — bare word is full-text search; quote it (shell claims `|`)
+Options: --limit <LIMIT> (unset = store default; bare word hits whole swarm),
+         --format <FORMAT> [default: message] (message = only `_msg`; json = raw NDJSON)
+```
+One subcommand (`query`) + `help`, three options total (`<LOGSQL>`, `--limit`,
+`--format`) — matches what's documented, nothing invented.
+
+## Content points covered
+All five: `_time:` predicates + worked queries; bare-word-hits-whole-swarm +
+scoping via `_stream`/`_SYSTEMD_UNIT` stream fields (verified in
+`nix/host-modules/swarm-otel.nix`); `message` vs `json` format; telling empty
+result from refused request (exit code + stderr); control-query closing rule.
+`_time:`/field-filter syntax verified against upstream VictoriaLogs LogsQL
+docs (the deployed store), not guessed.
+
+Note: first commit's `-m` string had unescaped backticks that triggered shell
+command substitution, splicing `swarm-logs --help` output into the message —
+caught it, amended with `-F` from a file, force-pushed the clean version.
+
+PR: https://forge.constellation.darkest.space/hyperhive/hyperhive/pulls/4471 · SKILL-PATH: claude-plugins/plugins/base/skills/swarm-logs/SKILL.md · HELP-VERIFIED: y · INVENTED-SYNTAX: none · TRAILER-CLEAN: y · VALE: pass
+
+**Subagent `skill-4460` stopped:** its turn ended and there was no goal to continue toward