refactor: remove SearXNG references and rename binary to kafka

- Rename cmd/searxng-go to cmd/kafka
- Remove all SearXNG references from source comments while keeping
  "SearXNG-compatible API" in user-facing docs
- Update binary paths in README, CLAUDE.md, and Dockerfile
- Update log message to "kafka starting"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/engines/braveapi.go

@@ -14,7 +14,7 @@ import (
 	"github.com/metamorphosis-dev/kafka/internal/contracts"
 )
 
-// BraveEngine implements the SearXNG `braveapi` engine (Brave Web Search API).
+// BraveEngine implements the `braveapi` engine (Brave Web Search API).
 //
 // Config / gating:
 // - BRAVE_API_KEY: required to call Brave
@@ -35,8 +35,8 @@ func (e *BraveEngine) Search(ctx context.Context, req contracts.SearchRequest) (
 		return contracts.SearchResponse{}, errors.New("brave engine not initialized")
 	}
 
-	// Gate / config checks should not be treated as fatal errors; SearXNG
-	// treats misconfigured engines as unresponsive.
+	// Gate / config checks should not be treated as fatal errors; the reference
+	// implementation treats misconfigured engines as unresponsive.
 	if strings.TrimSpace(e.apiKey) == "" {
 		return contracts.SearchResponse{
 			Query:               req.Query,
@@ -93,7 +93,7 @@ func (e *BraveEngine) Search(ctx context.Context, req contracts.SearchRequest) (
 		}
 	}
 
-	// SearXNG's python checks `if params["safesearch"]:` which treats any
+	// The reference implementation checks `if params["safesearch"]:` which treats any
 	// non-zero (moderate/strict) as strict.
 	if req.Safesearch > 0 {
 		args.Set("safesearch", "strict")