ref(mcp): make the dev-ACL instruction self-contained (no instance coupling)

Drop the '(This instance's rules carry the specifics.)' pointer — universal
_INSTRUCTIONS must not assume this install has a particular rulebook. State the
ACL principle on its own so it holds for any Scribe install/fork.

Refs plan 812 (instance-agnostic product principle).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/scribe/mcp/server.py

@@ -169,7 +169,7 @@ body); edit with update_process.
 
 When developing Scribe itself, honor its multi-user sharing ACL: scope every
 read and mutation of user data by owner + shares — never assume a single
-operator. (This instance's rules carry the specifics.)
+operator. "Works for one user" is not done.
 """