docs(6205): the remaining services files state the reason, not the instance that taught it

The 1-2 hit tail: access, background, backup, backup_job, canonical_systems,
design_stylesheet, forge_connections, moment_actions, notes, notifications,
placement, planning, platforms, projects, record_batch, recurrence,
report_check, retrieval_review, rule_scope, rule_versions, scheduler,
shape_check, supersession, system_rulings, system_usage, text, trash,
verification, version_pinning.

Also corrected while reading:
- backup.py said restore step 16 fills the System map; step 15 does.
- version_pinning.py pointed at a design doc that is not in the repo.

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

src/scribe/services/system_usage.py

@@ -1,6 +1,6 @@
 """System usage telemetry — were an area's rulings read once shown?
 
-The twin of `note_usage` and `rule_usage` for Systems (milestone 444). The
+The twin of `note_usage` and `rule_usage` for Systems. The
 rulings arm shows a System's rulings when a command or edit touches the
 System's files; a pull is somebody then opening the System (`get_system`). The
 ratio says whether delivering rulings by path earns its line.
@@ -97,8 +97,7 @@ async def usage_for_systems(system_ids: list[int]) -> dict[int, dict]:
     One GROUP BY for the whole list, never a query per row — this decorates a
     list view. Systems with no events come back as `empty_system_usage()`.
     Fails open: a readout that could break the Systems list is worse than a
-    zero, but the failure is reported so the zero is not mistaken for silence
-    (#2663).
+    zero, but the failure is reported so the zero is not mistaken for silence.
     """
     ids = [int(s) for s in system_ids]
     out: dict[int, dict] = {sid: empty_system_usage() for sid in ids}