feat(lessons): judged when written — a new lesson is offered its rules, and "no rule fits" is an answer (milestone 440 step 2, #4631)

"Which rule is this lesson an instance of?" now has three recorded answers:
a rule named (a confirmed link, #4630), no rule fits (new), or unjudged.

- Model + migration 0112: lesson_no_rule (lesson_id PK, CASCADE from the
  note; why; judged_at). A table rather than a key in notes.data, because
  that mirror is re-composed from the body on every edit and would erase it.
- Service (lesson_rules): set_no_rule rejects any confirmed link with the
  reason; a confirmation (set_lesson_rules or judge_link) deletes the answer;
  require_one_answer refuses both answers in one call before any write;
  judgments_for_lessons + attach_lesson_rules add rule_judgment (and no_rule)
  to every lesson payload; list_unjudged lists the open ones; rule_candidates
  searches rules with the lesson's claim + trigger at the explicit-search bar,
  None when the search could not run.
- MCP: create_lesson/update_lesson take no_rule; an unanswered create returns
  rule_candidates, rule_judgment and a rule_hint; list_lessons(unjudged=true).
- REST: the same on POST/PATCH /api/lessons and GET ?unjudged=1; create
  returns rule_candidates.
- Backup v19: a lesson_no_rule section, export (full and per-user) and import.
- Guidance: create_lesson docstring, writing-records.md in using-scribe (owner,
  pinned in test_guidance_ownership), create_rule docstring on linking the
  lessons a new rule governs. Plugin version minted.
- Tests: door units, integration for the three states, the rejection reason,
  scoping, cascade; backup registries.

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

src/scribe/mcp/tools/rulebooks.py

@@ -393,6 +393,14 @@ async def create_rule(
     observations belong, and the reason the kind question is worth asking
     out loud rather than settled silently before the proposal.
 
+    A RULE WRITTEN FOR A SITUATION LESSONS ALREADY RECORD is linked from
+    them once it exists: `update_lesson(lesson_id, rule_ids=[…, <new id>])`
+    for each lesson it governs. Those lessons are the concrete situations
+    that proved it, and linked, they are how the rule is reached in moments
+    closer to why it was written than its own wording. A lesson that
+    answered "no rule fits" before this rule existed is the first to
+    re-judge; `get_lesson` shows the answer and its reason.
+
     Where the interface offers structured choices, ask it that way — a
     question with named options is answered in a click, while the same
     question inside a paragraph is answered by scrolling past. Where it does