feat(alerts): a rule can fire when a reading rises, "rose by N" (#6724)

A rule compared a reading with a fixed number, so Synology Disk 1's bad
sectors going from 3,160 to 3,392 could say nothing: a count that only grows
is soon past any line. "rose by" compares each reading with the one before it,
kept on the alert's state and only for such a rule. A fall (a replaced disk)
doesn't fire. On the rule form, through MCP, and worded in emails, the alert
sentence, history and the timeline.

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

steward/mcp/tools/hosts.py

@@ -190,7 +190,7 @@ async def get_host(host: str, parts_limit: int = 20) -> dict:
         {
             "rule_id": rule.id, "rule_name": rule.name, "state": alert_svc.alert_label(state),
             "resource": rule.resource_name, "metric": rule.metric_name,
-            "condition": f"{rule.metric_name} {rule.operator.value} {rule.threshold:g}",
+            "condition": f"{rule.metric_name} {rule.operator.said} {rule.threshold:g}",
             "since": iso(state.last_transition_at), "age_s": age_s(state.last_transition_at),
         }
         for state, rule in active