feat(rules)!: retire rulebook subscriptions and per-project suppressions (#4052)

A rule's home is its scope now: a rule in a rulebook topic is global, a rule on
a project applies to that project, and retrieval reads that directly (#4074).
A subscription had stopped changing anything a session received; a suppression
muted rules from a subscription. Operator, 2026-09-15: "we have global and
project scoped rules, we don't need the subscriptions now."

What goes, whole (rule 22):
- Migration 0101 drops project_rulebook_subscriptions, project_rule_suppressions
  and project_topic_suppressions, and strips subscribe_rulebooks (and 394's
  leftover exclude_always_on_rulebooks) from stored inception choices.
- Service, MCP and REST: subscribe/unsubscribe and the four suppress/unsuppress
  operations. The Subscribers checklist, the subscribe chips, the skip buttons
  and the Suppressed section in the rules UI.
- Inception asks two questions (design system, seed Systems). create_project and
  decide_project_inception lose subscribe_rulebooks.
- Backup v15 stops exporting the three sections; older archives still restore,
  the keys simply unread. Trash no longer hard-deletes suppression rows.

What changes meaning:
- get_applicable_rules is a project's LISTING: its own rules, plus the global
  rules tagged to an area it works in. Untagged global rules apply everywhere
  and arrive by retrieval, so they are not listed. A co_surfaces partner on a
  different project is not dragged in.
- list_rules(project_id) lists that project's own rules.
- rules_payload drops subscribed_rulebooks and suppressed_*; the handshake's
  brief form is project_rules alone.
- using-scribe's "Where a new rule goes" and inception sections, tool
  docstrings and docs say global vs project. Plugin 2026.09.15.1620.

Milestone 414 step 2.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

tests/test_services_planning.py

@@ -13,7 +13,7 @@ async def test_start_planning_creates_milestone_and_returns_rules():
         "rules": [{"id": 1, "title": "dev is home", "statement": "...",
                    "topic_title": "git-workflow", "rulebook_title": "FabledSword family"}],
         "truncated": False,
-        "subscribed_rulebooks": [{"id": 2, "title": "FabledSword family"}],
+        "project_rules": [{"id": 3, "title": "own", "statement": "..."}],
     }
     with patch("scribe.services.planning.milestones_svc.create_milestone",
                AsyncMock(return_value=fake_milestone)) as mock_create, \
@@ -34,7 +34,8 @@ async def test_start_planning_creates_milestone_and_returns_rules():
     # Returned shape
     assert out["milestone"]["id"] == 5
     assert out["applicable_rules"][0]["title"] == "dev is home"
-    assert out["subscribed_rulebooks"] == [{"id": 2, "title": "FabledSword family"}]
+    assert out["project_rules"][0]["id"] == 3
+    assert "subscribed_rulebooks" not in out
     assert out["open_task_count"] == 3