rename: kafka → samsa

Full project rename from kafka to samsa (after Gregor Samsa, who
woke one morning from uneasy dreams to find himself transformed).

- Module: github.com/metamorphosis-dev/kafka → samsa
- Binary: cmd/kafka/ → cmd/samsa/
- CSS: kafka.css → samsa.css
- UI: all 'kafka' product names, titles, localStorage keys → samsa
- localStorage keys: kafka-theme → samsa-theme, kafka-engines → samsa-engines
- OpenSearch: ShortName, LongName, description, URLs updated
- AGPL headers: 'kafka' → 'samsa'
- Docs, configs, examples updated
- Cache key prefix: kafka: → samsa:

internal/autocomplete/service.go

@@ -1,4 +1,4 @@
-// kafka — a privacy-respecting metasearch engine
+// samsa — a privacy-respecting metasearch engine
 // Copyright (C) 2026-present metamorphosis-dev
 //
 // This program is free software: you can redistribute it and/or modify
@@ -102,7 +102,7 @@ func (s *Service) wikipediaSuggestions(ctx context.Context, query string) ([]str
 	}
 	req.Header.Set(
 		"User-Agent",
-		"gosearch-go/0.1 (compatible; +https://github.com/metamorphosis-dev/kafka)",
+		"gosearch-go/0.1 (compatible; +https://github.com/metamorphosis-dev/samsa)",
 	)
 
 	resp, err := s.http.Do(req)