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/views/templates/opensearch.xml

@@ -1,12 +1,12 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/">
-  <ShortName>kafka</ShortName>
+  <ShortName>samsa</ShortName>
   <Description>A privacy-respecting, open metasearch engine</Description>
   <InputEncoding>UTF-8</InputEncoding>
   <OutputEncoding>UTF-8</OutputEncoding>
-  <LongName>kafka — Privacy-respecting metasearch</LongName>
+  <LongName>samsa — Privacy-respecting metasearch</LongName>
   <Image width="16" height="16" type="image/svg+xml">/static/img/favicon.svg</Image>
-  <Contact>https://git.ashisgreat.xyz/penal-colony/kafka</Contact>
+  <Contact>https://git.ashisgreat.xyz/penal-colony/samsa</Contact>
   <Url type="text/html" method="GET" template="{baseUrl}/search?q={searchTerms}&amp;format=html">
     <Param name="pageno" value="{startPage?}" />
     <Param name="language" value="{language?}" />