feat: add actions CLI module for distributed actions registry

Adds @backstage/cli-module-actions with commands for listing and executing
actions from the distributed actions registry. Exports auth helpers from
cli-module-auth for cross-module reuse. Relaxes the actions registry auth
check to allow direct user invocations from the CLI.

Signed-off-by: benjdlambert <ben@blam.sh>

.changeset/add-actions-cli-module.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli-module-actions': patch
+---
+
+Added `actions` CLI module for listing and executing actions from the distributed actions registry. Includes `actions list`, `actions execute`, and `actions sources` commands for managing plugin sources.

.changeset/allow-user-action-invocation.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-defaults': patch
+---
+
+The actions registry invoke endpoint now accepts direct user credentials in addition to service principals, enabling CLI and other direct user clients to invoke actions.

.changeset/auth-module-exports.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli-module-auth': patch
+---
+
+Export auth helper utilities for use by other CLI modules. Added per-instance config storage with `getInstanceConfig` and `updateInstanceConfig`.

.changeset/cli-defaults-actions.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli-defaults': patch
+---
+
+Added `@backstage/cli-module-actions` to the default set of CLI modules.