grafana: shorten logstore's 'no severity' panel description

Slipped past the #4574 lint — 1473 chars vs. the 100-char cap, caught
by pre-push while working on an unrelated branch. Same treatment as
every other panel: state what the number is, not the reasoning.

nix/host-modules/swarm-grafana/dashboards/logstore.json

@@ -492,7 +492,7 @@
       "id": 9,
       "type": "timeseries",
       "title": "Log rows with no severity (must be zero)",
-      "description": "This panel is a check rather than a view: the collector maps journald's PRIORITY onto an OpenTelemetry severity at every tier, and this is what says out loud whether a line got one. Both series are rows whose `severity_text` is absent or the literal `Unspecified`, which is what VictoriaLogs stores when nothing set a severity — split by whether the row had a PRIORITY to map in the first place.\n\n**`journald_priority_unmapped`** is a row that carries PRIORITY and still arrived without a severity. It is the regression line: nonzero means a journald receiver somewhere lost its severity_parser operator, so read it against `nix/journald-severity.nix` and the two receivers that import it.\n\n**`no_priority_field`** is a row that never had a priority — today that is Claude Code's own OTLP telemetry (`scope.name: com.anthropic.claude_code.events`), which emits log records with no severity set at the source. Mapping cannot reach it; it needs a fix where it is produced, so this series is expected nonzero until that lands and is NOT evidence the mapping broke.\n\nRange-scoped over time on purpose. An instantaneous zero is also what a broken query returns — a line you can watch go to zero and stay there is the part that survives whoever wrote it. To sanity-check the query itself, read it against `Rows in range · all sources (control)` above: that panel nonzero while both of these are flat zero means these queries stopped matching, not that every line grew a severity.",
+      "description": "Rows missing severity_text, split by whether PRIORITY was present to map.",
       "datasource": {
         "type": "victoriametrics-logs-datasource",
         "uid": "@logsDatasourceUid@"