docs(6856): the plugin's guidance and the docs say what a session may do in another project

using-grimoire, which owns cross-project conduct, now says the one change
to make toward another project is filing an issue with how it was found
and the evidence, and that the plugin asks before anything more. The
features page describes the fence.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugin/skills/using-grimoire/SKILL.md

@@ -280,7 +280,12 @@ bound — confine the session to it:
 - **Only reference or offer work on the in-scope project.** Don't surface,
   suggest, or start work on other projects unless the operator explicitly widens
   scope.
-- If something clearly belongs to a *different* project, say so and **ask before
+- **Toward another project, the one change to make is filing an issue**:
+  `create_task(project_id=<theirs>, kind="issue")`, carrying how you found it
+  and the evidence. Editing its files, committing or pushing in its repo, and
+  changing its other records are the operator's call, and the plugin asks them
+  before any of those runs. Reading anything there is fine.
+- If the work itself belongs to a *different* project, say so and **ask before
   switching** — never silently operate cross-project.
 
 ## Read these when the moment comes