Remove SearXNG search backend, use Firecrawl exclusively

SearXNG was a fallback search backend that added complexity without
being used in practice. All search-dependent features (web search,
government DB checks, vetting orchestrator, tracker mapping) now use
Firecrawl exclusively. Removes the SEARCH_ENDPOINT config plumbing
from probodconfig, bootstrap, Helm charts, and all callers.

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

pkg/probodconfig/config.go

@@ -67,7 +67,6 @@ type (
 		Agents            AgentsConfig            `json:"llm"`
 		EvidenceDescriber EvidenceDescriberConfig `json:"evidence-describer"`
 		ChromeDPAddr      string                  `json:"chrome-dp-addr"`
-		SearchEndpoint    string                  `json:"search-endpoint"`
 		Firecrawl         FirecrawlConfig         `json:"firecrawl"`
 		CustomDomains     CustomDomainsConfig     `json:"custom-domains"`
 		SCIMBridge        SCIMBridgeConfig        `json:"scim-bridge"`