Reuse mapping agent to attribute trackers in enricher

The enrichment worker no longer invents a description when a tracker's
purpose cannot be substantiated; it records an empty description and
marks the row enriched so the stale-recovery loop does not retry it.

Vendor identification is the mapping pipeline's job, so the enricher
reuses the existing tracker-mapping agent to attribute a third party
for an unlinked common pattern before describing it. A confident
catalog match seeds the enrichment prompt and links the pattern, but
the enricher never creates or overrides an attribution.

When a blank, unlinked catalog row later gains a third party through
the mapping pipeline's upsert, enrichment is re-armed so the now-known
vendor gets a second, better-informed description attempt.

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

pkg/cookiebanner/common_pattern_enrichment_agent.go

@@ -32,7 +32,7 @@ var trackerEnrichmentPrompt string
 // CommonPatternEnrichmentResult is the structured output the
 // common-pattern enrichment agent returns.
 type CommonPatternEnrichmentResult struct {
-	Description string `json:"description" jsonschema:"A concise, factual, compliance-grade description of what this tracker stores or does and its purpose. One or two sentences. Name the operating company when known."`
+	Description string `json:"description" jsonschema:"A concise, factual, compliance-grade description of what this tracker stores or does and its purpose. One or two sentences. Name the operating company when known. Empty when the purpose cannot be substantiated from evidence."`
 }
 
 func buildCommonPatternEnrichmentAgent(