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/mcp/tools/rulebooks.py

@@ -18,7 +18,7 @@ from scribe.mcp._context import current_user_id
 from scribe.services import dedup as dedup_svc
 from scribe.services import rulebooks as rulebooks_svc
 from scribe.services import trash as trash_svc
-from scribe.services.rule_usage import record_rule_pulled, record_rule_surfaced
+from scribe.services.rule_usage import record_rule_pulled
 
 
 # ── Rulebook CRUD ───────────────────────────────────────────────────────
@@ -249,7 +249,7 @@ async def create_rule(
     topic_id: int, title: str, statement: str, when_to_apply: str = "",
     why: str = "", how_to_apply: str = "", order_index: int = 0,
     arose_from_id: int = 0, verify_with: str = "", expires_when: str = "",
-    force: bool = False,
+    system_ids: list[int] | None = None, force: bool = False,
 ) -> dict:
     """Create a new rule in a rulebook (a SHARED rule — keep it general).
 
@@ -415,7 +415,7 @@ async def create_project_rule(
     project_id: int, statement: str, title: str = "", when_to_apply: str = "",
     why: str = "", how_to_apply: str = "", order_index: int = 0,
     arose_from_id: int = 0, verify_with: str = "", expires_when: str = "",
-    force: bool = False,
+    system_ids: list[int] | None = None, force: bool = False,
 ) -> dict:
     """Create a rule scoped to a single project (no rulebook needed).