cli-node: add CliAuth class for shared CLI authentication

Introduces a class-based authentication management API in @backstage/cli-node
that reads the on-disk instance store, transparently refreshes expired tokens,
and provides a convenient surface for other CLI modules to consume.

The split keeps filesystem-based instance selection and writes owned by
cli-module-auth, while reading and consuming the current instance is
available through CliAuth in cli-node.

Migrates cli-module-actions to use the new API and deprecates the ad-hoc
function exports from cli-module-auth.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

yarn.lock

@@ -3159,12 +3159,16 @@ __metadata:
     chalk: "npm:^4.0.0"
     commander: "npm:^12.0.0"
     fs-extra: "npm:^11.2.0"
+    keytar: "npm:^7.9.0"
     pirates: "npm:^4.0.6"
     semver: "npm:^7.5.3"
     yaml: "npm:^2.0.0"
     zod: "npm:^3.25.76 || ^4.0.0"
   peerDependencies:
     "@swc/core": ^1.15.6
+  dependenciesMeta:
+    keytar:
+      optional: true
   peerDependenciesMeta:
     "@swc/core":
       optional: true