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

frontend/src/api/inception.ts

@@ -2,7 +2,6 @@
 import { apiGet, apiPost } from "@/api/client";
 
 export interface InceptionChoices {
-  subscribe_rulebooks: number[];
   design_system_id: number | null;
   seed_systems: boolean;
 }
@@ -15,8 +14,6 @@ export interface InceptionRecord {
 }
 
 export interface InceptionDefaults {
-  rulebooks: { id: number; title: string }[];
-  subscribed_rulebooks: { id: number; title: string }[];
   design_system_id: number | null;
   design_systems: { id: number; title: string }[];
   systems: number;
@@ -25,11 +22,11 @@ export interface InceptionDefaults {
 export interface InceptionDecision {
   project_id: number;
   inception: InceptionRecord;
-  effects: { excluded: number[]; subscribed: number[]; design_system_id: number | null; systems_seeded: string[] };
+  effects: { design_system_id: number | null; systems_seeded: string[] };
 }
 
 export const emptyChoices = (): InceptionChoices => ({
-  subscribe_rulebooks: [], design_system_id: null, seed_systems: false,
+  design_system_id: null, seed_systems: false,
 });
 
 export const fetchInceptionDefaults = (projectId: number) =>