otel: map journald PRIORITY onto a severity at every journald receiver

Records reached VictoriaLogs carrying the journal's raw PRIORITY and
severity_text "Unspecified" — every line in the store, at every tier, with
no level a query or a dashboard could read. VictoriaLogs has no ingest
parameter naming a level field; it auto-detects one by field name, so the
mapping has to happen in the collector.

A stanza severity_parser on each journald receiver, from one shared file
rather than a copy per tier: the two receivers are unrelated config (a
fixed stanza in the agent container, a parameterised block inside the
swarm-otel container) and a drifted copy fails silently — every line still
arrives, labelled as the wrong thing.

Two details that are easy to get wrong and quiet when wrong. PRIORITY
counts down in urgency where the OTEL severity counts up, so the table is
written as a table. And overwrite_text is required: without it the parser
sets the severity number and leaves the text as the raw digit, so
severity_text arrives as the literal "6" — populated, and not a level
anything renders.

nix/host-modules/swarm-otel.nix

@@ -1208,6 +1208,16 @@ in
                   journald = {
                     directory = hostJournalDir;
                     units = cfg.journaldUnits;
+                    # The SAME operator list the agent tier attaches to its own
+                    # receiver (nix/agent-modules/otel.nix), and it transfers
+                    # without adjustment: the entry shape is the receiver's,
+                    # not the journal's. Both are this one component running
+                    # `journalctl -o json`, so `PRIORITY` is spelled and typed
+                    # identically whether the directory it was pointed at holds
+                    # a host's journal or a container's. What differs between
+                    # the two receivers is which journal and which units —
+                    # neither of which the parser reads.
+                    operators = import ../journald-severity.nix;
                   };
                 };