feat(rules): both doors carry the trigger, the tier, the areas and the edges (#3029, milestone 307 step 3, surfaces)

MCP and REST both gain when_to_apply / tier / system_ids / arose_from_id on
create and update, plus relate_rules / unrelate_rules for the typed edges, and
get_rule now returns a rule's areas and relations alongside it.

rule_detail() is a SERVICE function, not one per door. It started as a copy in
each — identical, and the prior-art hook flagged it immediately, which is the
same lesson rules_payload (#2858) already recorded: a second copy drifts. Both
doors call the one seam, so create, update and get cannot disagree about what a
rule looks like coming back.

The authoring guidance lands in create_rule's docstring rather than in a rule,
per rule 119 as the operator described it: this is behaviour every instance
should inherit, not one operator's preference. It states the test —

  ONE RULE = ONE THING YOU COULD VIOLATE. Rules that FAIL TOGETHER get linked
  with relate_rules(kind="co_surfaces"), never merged into one row.

— and names why merging loses: a merged rule cannot be cited, surfaced or
suppressed a clause at a time, and it grows without limit because adding to it
is always cheaper than adding a rule. create_project_rule says the same about
"overrides", which is what FabledCurator's 85/86 should have been instead of
near-copies that drift from their parent.

The tier arg carries the test itself: can you name the trigger WITHOUT naming a
system, an artifact type or a moment? If the honest answer is "whenever you are
working", it is always_on.

Tests: the applicable-rules cases fabricated raw tuples matching the old column
lists, so they move to the entity shape via fake_rule; new cases pin rule_brief
(a DATE not a stamp, the depth left to get_rule, no null keys) and that an
unknown tier falls back to BINDING. fake_rule gains when_to_apply / tier /
arose_from_id for the note-2109 reason the helper exists: unnamed, they would
be truthy MagicMocks. The tool tests stub the new rule_detail seam — they are
about argument forwarding and have no database.

The module header's "Sixteen tools" had been wrong for two milestones; the
registration count test is what actually catches that, so the header now says
so instead of carrying a number.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/helpers.py

@@ -153,8 +153,12 @@ def fake_topic(**attrs) -> MagicMock:
 
 def fake_rule(**attrs) -> MagicMock:
     return _with_defaults({
-        "id": 1, "topic_id": 10, "title": "dev is home",
+        "id": 1, "topic_id": 10, "project_id": None, "title": "dev is home",
         "statement": "Work directly on dev", "why": "", "how_to_apply": "",
+        # Named for the note-2109 reason the whole helper exists: unnamed,
+        # `when_to_apply` and `arose_from_id` would be truthy MagicMocks and
+        # rule_brief would attach both keys on every stand-in.
+        "when_to_apply": None, "tier": "always_on", "arose_from_id": None,
         "order_index": 0, "created_at": _now(), "updated_at": _now(),
     }, attrs)