Add select-mode, version, pack and publish sub-actions (#656)

* Add select-mode, version, and publish sub-actions

* Rename

* No github-token needed for select-mode for now

* extend select-mode with publish-plan check and upload

* Rename base-branch to pr-base-branch

* add `pack` subaction

* `--from-pack` support in the publish subaction

* rename CLI arg

* update rolldown config

* rename pack dir input/output

* tweak retendion days

---------

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

select-mode/action.yml

@@ -0,0 +1,14 @@
+name: Changesets - Select Mode
+description: Whether to version or publish in the current repo state
+runs:
+  using: node24
+  main: ../dist/select-mode.js
+inputs: {}
+outputs:
+  mode:
+    description: "The mode to use for the current repo state: 'version', 'publish', or 'none'."
+  publish-plan-artifact-id:
+    description: "Artifact id for the generated publish plan when mode is `publish`"
+branding:
+  icon: package
+  color: blue