Restore tracker mapping linking, drop only create

The tracker-mapping worker had been reduced to catalog resolution only,
which removed not just the auto-creation of an org ThirdParty but also
the auto-linking of an existing one. Only the creation needed to go: it
raced the load-then-create check and produced duplicate vendors.

Restore the full org ThirdParty resolution (exact common-id link,
sibling direct-link, high-confidence heuristic, and the disambiguation
agent) and remove only the CreateFromCommon branch and its
categorisation gate. When nothing matches, the worker now leaves
third_party_id unset rather than creating a vendor; creation happens
exclusively through the explicit ImportFromCommon action. Drop the
now-dead CreateFromCommon helper and rename match.go to common_match.go.

Fix a latent test bug surfaced by actually running the DB-backed suite
(skipped in CI without Postgres): the heuristic-match candidate lacked
Level 1, so the level-filtered candidate loader excluded it and the old
fallback create masked the miss.

Signed-off-by: Émile Ré <emile@probo.com>

pkg/probod/probod.go

@@ -321,7 +321,7 @@ func (impl *Implm) Run(
 		return err
 	}
 
-	trackerMappingCfg, trackerEnrichmentCfg, err := impl.buildTrackerAgents(l, tp, r)
+	trackerMappingCfg, trackerEnrichmentCfg, thirdPartyDisambiguationCfg, err := impl.buildTrackerAgents(l, tp, r)
 	if err != nil {
 		return err
 	}
@@ -775,6 +775,7 @@ func (impl *Implm) Run(
 		pgClient,
 		l,
 		trackerMappingCfg,
+		thirdPartyDisambiguationCfg,
 		time.Duration(impl.cfg.TrackerMappingWorker.StaleAfter)*time.Second,
 		worker.WithInterval(time.Duration(impl.cfg.TrackerMappingWorker.Interval)*time.Second),
 		worker.WithMaxConcurrency(impl.cfg.TrackerMappingWorker.MaxConcurrency),