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_inception.py

@@ -3,10 +3,9 @@
 The WHY a project inherits what it does lives on projects.inception. Pure
 validation is pinned here; the effects are step 3's integration tests.
 
-The opt-out of an always-on rulebook had its own association table until
-milestone 394. With no always-on tier there is nothing to opt out OF — a
-rulebook binds a project only by subscription — so the table and the test
-that pinned its shape both went with it.
+Rules left inception in two steps: the always-on opt-out with the tier
+(milestone 394), and the rulebook subscription with subscriptions (milestone
+414). A rule in a rulebook is global, so there is nothing to choose.
 """
 from scribe.models.project import Project
 from scribe.services.inception import (
@@ -28,10 +27,9 @@ def test_project_carries_an_inception_record_and_to_dict_shows_it():
 
 
 def test_validate_inception_pins_the_choice_vocabulary():
-    assert CHOICE_KEYS == ("subscribe_rulebooks", "design_system_id", "seed_systems")
+    assert CHOICE_KEYS == ("design_system_id", "seed_systems")
     assert validate_inception({}) is None
-    assert validate_inception({"subscribe_rulebooks": [2],
-                               "design_system_id": 3, "seed_systems": True}) is None
+    assert validate_inception({"design_system_id": 3, "seed_systems": True}) is None
     assert validate_inception({"design_system_id": None}) is None
     assert "must be an object" in validate_inception([])
     assert "unknown inception choice" in validate_inception({"repo": "x"})
@@ -41,19 +39,17 @@ def test_validate_inception_pins_the_choice_vocabulary():
     # believe a rulebook had been declined.
     assert "unknown inception choice" in validate_inception(
         {"exclude_always_on_rulebooks": [1]})
-    assert "list of rulebook ids" in validate_inception({"subscribe_rulebooks": [0]})
-    assert "list of rulebook ids" in validate_inception({"subscribe_rulebooks": [True]})
+    # Same for the subscription choice since milestone 414.
+    assert "unknown inception choice" in validate_inception({"subscribe_rulebooks": [2]})
     assert "positive id or null" in validate_inception({"design_system_id": 0})
     assert "positive id or null" in validate_inception({"design_system_id": True})
     assert "true or false" in validate_inception({"seed_systems": "yes"})
 
 
 def test_normalize_choices_is_canonical_and_complete():
-    out = normalize_choices({"subscribe_rulebooks": [3, 1, 3]})
-    assert out == {"subscribe_rulebooks": [1, 3],
-                   "design_system_id": None, "seed_systems": False}
-    assert normalize_choices(None) == {"subscribe_rulebooks": [],
-                                       "design_system_id": None, "seed_systems": False}
+    out = normalize_choices({"design_system_id": 4})
+    assert out == {"design_system_id": 4, "seed_systems": False}
+    assert normalize_choices(None) == {"design_system_id": None, "seed_systems": False}
 
 
 def test_standard_systems_vocabulary_reads_the_catalog_not_a_constant():