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.

crates/bindings/npm/README.md

@@ -4,11 +4,11 @@ Turn a pile of files into a searchable corpus: chunking, scrubbing, subtitles
 and rank fusion, as WebAssembly.
 
 ```sh
-npm install catena
+npm install catena-corpus
 ```
 
 ```js
-import { chunkMarkdown, scrub, countTokens, fuseHits } from "catena";
+import { chunkMarkdown, scrub, countTokens, fuseHits } from "catena-corpus";
 
 const chunks = chunkMarkdown(markdown, 512, 64);
 chunks[0].page;      // 41
@@ -60,7 +60,7 @@ at compile time. Those stay command-line tools.
 ## Node and the web
 
 ```js
-import { chunkMarkdown } from "catena";        // resolves per environment
+import { chunkMarkdown } from "catena-corpus";        // resolves per environment
 import { chunkMarkdown } from "catena/node";   // or pick one
 import { chunkMarkdown } from "catena/web";
 ```