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/engines/bing_test.go

@@ -7,7 +7,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/metamorphosis-dev/kafka/internal/contracts"
+	"github.com/metamorphosis-dev/samsa/internal/contracts"
 )
 
 func TestBingEngine_EmptyQuery(t *testing.T) {