feat: add plugin packing, signing, pinned trust and tmxplug bundling

packages/plugin-sdk/README.md

@@ -0,0 +1,19 @@
+# @termix/plugin-sdk
+
+Everything a [Termix](https://github.com/Termix-SSH/Termix) plugin builds
+against: the types for `activate(ctx)` and `activate(app)`, table
+definitions, the manifest schema, test helpers, a vitest preset and the
+`termix-plugin` CLI.
+
+```bash
+npm install --save-dev @termix/plugin-sdk
+npx termix-plugin build      # bundle dist/backend.js and dist/frontend.js
+npx termix-plugin test       # run the plugin's vitest suite
+npx termix-plugin validate   # check manifest.json and the files it names
+npx termix-plugin pack       # write <id>-<version>.tmxplug
+npx termix-plugin sign <file.tmxplug>   # needs TERMIX_PLUGIN_SIGNING_KEY
+```
+
+Start from
+[Termix-Plugin-Template](https://github.com/Termix-SSH/Termix-Plugin-Template).
+The full contract is in [ARCHITECTURE.md](./ARCHITECTURE.md).