fix(retrieval): the rules never-opened warning stops sending the reader to a review tool that refuses rules (#4798)

#4798 "The rules corpus's surfaced_never_pulled warning sends the reader to
menus_to_review, which can only review auto_inject". #4772 gave the warning
one remedy for both corpora: "judge a sample with menus_to_review". That is
right for notes, where a line carries its passage. For rules it is a dead
end: retrieval_review.REVIEWABLE holds only auto_inject, so the tool
refuses every rule arm.

- The reading is now per corpus (_NEVER_PULLED_READING). For rules, the
  text says:
  - the count includes rules that only arrived in a listing;
  - a rule can rightly be set aside on its trigger alone;
  - no judged sample exists for the rule arms;
  - a rule set aside again and again is a trigger to fix (update_rule
    when_to_apply, then what_might_apply), not a floor.
- The tool docstring says the same.
- The guard is tied to REVIEWABLE, so it can fail in both directions: if
  the rules text names menus_to_review while no rule arm is reviewable, or
  if a rule arm becomes reviewable and the text still says there is no
  sample.

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

src/scribe/mcp/tools/search.py

@@ -624,6 +624,8 @@ It is an UPPER BOUND per surface: a pull records the door it came
       corpus. Not a verdict on them: a line carries its matched passage, so
       an unopened record may have been unrelated, enough as shown, or already
       in context. Judge a sample (`menus_to_review`) before acting on it.
+      For RULES there is no judged sample: a rule set aside again and again
+      is a trigger to fix (`update_rule(when_to_apply=...)`), not a floor.
     - `read_and_unacted` — distinct rules OPENED in the window that recorded
       no outcome, against the ones that did. The failure milestone 419 was
       opened on, and the worse sibling of `surfaced_never_pulled` above: a