publish as catena-corpus on PyPI and npm

Both registries already have a `catena`: an HPE blockchain client on PyPI,
and a JavaScript OOP wrapper at 2.2.0 on npm. Neither is going anywhere, so
the distributions take a name that is free on both.

The Python import is unaffected — a distribution name and a module name are
independent there, so `pip install catena-corpus` still gives `import
catena`, and nothing in the examples or the bindings changes. On npm the
package name is the import specifier, so that one does change: `import
{ chunkMarkdown } from "catena-corpus"`.

The crates keep their own names. `catena` is free on crates.io.

examples/typescript/src/episode-to-chapters.ts

@@ -11,7 +11,7 @@
 // broadcast — a work of the US government, so public domain.
 
 import { readFileSync } from "node:fs";
-import { parseSubtitles, segmentCues, packCues, countTokens } from "catena";
+import { parseSubtitles, segmentCues, packCues, countTokens } from "catena-corpus";
 
 const SAMPLE = `WEBVTT
 

examples/typescript/src/search-and-rerank.ts

@@ -12,7 +12,7 @@
 // vector database and whatever else. What they came from does not matter
 // here; only where each of them placed does.
 
-import { fuseHits, type Hit } from "catena";
+import { fuseHits, type Hit } from "catena-corpus";
 
 // `payload` is whatever you want carried alongside — rrf hands it back
 // untouched, so a hit can arrive here with the row it came from attached.