feat(rulebook): augment get_project with applicable_rules + MCP instructions

src/fabledassistant/mcp/server.py

@@ -20,6 +20,16 @@ Hierarchy: Project -> Milestone -> Task/Note.
   unchanged on updates.
 - For optional integer FKs (project_id, milestone_id, parent_id), use 0 to mean
   "not set".
+
+Scribe maintains a Rulebook system (Rulebook -> Topic -> Rule). Rules carry
+an actionable statement plus optional Why and How-to-apply context. When you
+start work on a project, get_project(id) returns applicable_rules (the rules
+from rulebooks the project subscribes to) and subscribed_rulebooks. Consult
+these before making decisions about workflow, conventions, or scope. Full
+text (Why / How-to-apply) is available via get_rule(id). You may create new
+rules via create_rule when you notice a pattern worth codifying — coordinate
+with the operator on whether it belongs in an existing rulebook+topic or a
+new one.
 """