fix(host-agent): a large update records its package count (#6794)

The root helper counted updated packages from the last 2,000 characters
of the package manager's output. Every manager prints its count (apt's
"N upgraded, N newly installed", dnf's "Upgrade N Packages", zypper's
"N packages to upgrade", pacman's "Packages (N)") before the long log of
what it then does, so a large update pushed the line out of the tail
and the job recorded no count. Docker03's 2026-11-01 job applied 17
updates and reported none; Docker02's single package was counted.

The update steps now read their whole output (run(keep=None)), and only
the failure text and the job's detail are cut short. Agent 1.26.1, so
hosts show the helper as an update to take.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/host_agent/agent.py

@@ -22,7 +22,7 @@ from collections import deque
 from concurrent.futures import ThreadPoolExecutor, wait as wait_futures
 from datetime import datetime, timezone
 
-AGENT_VERSION = "1.26.0"
+AGENT_VERSION = "1.26.1"
 
 # Default path to the local Docker Engine socket. Overridable via the
 # `docker_socket` config key; collection is silently skipped if it's absent or