Add tracker description enrichment worker

Tracker descriptions were only filled on the agent-identification path,
so patterns resolved by domain, sibling, or fallback stayed without one,
and empty mapping upserts could clobber a researched description on the
shared catalog row.

Move description ownership to a dedicated, global common-pattern
enrichment worker. New catalog rows are queued on insert; the worker
researches a compliance-grade description with web search, records it on
the common pattern, and fans it out to every linked tracker pattern. The
mapping worker no longer generates descriptions and only propagates an
already-enriched one at link time.

Rename TrackerMappingConfig to TrackerAgentsConfig since the mapping and
enrichment agents now share it.

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

pkg/cookiebanner/prompts/tracker_identification.txt.tmpl

@@ -8,7 +8,6 @@ Given a tracker pattern (cookie name, local storage key, etc.), its type, max-ag
 Return a structured JSON response with:
 - third_party_name: the canonical company/service name (e.g. "Google Analytics", not "google" or "GA")
 - category: the business category of the third party
-- description: a one-sentence description of what this tracker does
 - confidence: how confident you are in the identification (0.0 to 1.0)
 </task>