fix(rules): restore system_ids and clear the imports the deletions orphaned (#394)

Three defects from the sweep, all caught by ruff.

system_ids was REMOVED FROM create_rule AND create_project_rule — a real API
regression, not a lint nit. The parameter shared a signature line with tier,
so deleting the tier deleted it too, and the tools lost the ability to tag a
new rule to an area. Areas are what let a rule reach a project after this
milestone, so the one parameter that decides reach went missing from the two
tools that create reachable rules.

The other two are imports left holding nothing: services/rulebooks.py's
module-level datetime and its IntegrityError were used only by functions this
milestone deleted, and plugin_context lost four (select, async_session,
RulebookTopic, rulebooks_svc) with the preload and _topic_titles.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011cPyzNnegXHr5iRMzzy5KJ

src/scribe/services/plugin_context.py

@@ -18,15 +18,11 @@ import logging
 import re
 import time
 
-from sqlalchemy import select
 
-from scribe.models import async_session
-from scribe.models.rulebook import RulebookTopic
 from scribe.services import design_systems as design_systems_svc
 from scribe.services import knowledge as knowledge_svc
 from scribe.services import notes as notes_svc
 from scribe.services import projects as projects_svc
-from scribe.services import rulebooks as rulebooks_svc
 from scribe.services import shape_ledger as shape_ledger_svc
 from scribe.services import snippets as snippets_svc
 from scribe.services.access import label_shared_items, owner_names_for