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/rulebooks.ts

@@ -108,23 +108,7 @@ export interface ApplicableRules {
     rulebook_title: string;
   })[];
   project_rules: RuleHeader[];
-  suppressed_rules: {
-    id: number;
-    title: string;
-    topic_id: number;
-    topic_title: string;
-    rulebook_id: number;
-    rulebook_title: string;
-  }[];
-  suppressed_topics: {
-    id: number;
-    title: string;
-    rulebook_id: number;
-    rulebook_title: string;
-  }[];
   truncated: boolean;
-  subscribed_rulebooks: { id: number; title: string }[];
-  /** Always-on rulebooks this project opted out of at inception (milestone 297). */
 }
 
 // ── Rulebooks ───────────────────────────────────────────────────────
@@ -272,15 +256,7 @@ export async function deleteRule(id: number): Promise<void> {
   return apiDelete(`/api/rules/${id}`);
 }
 
-// ── Subscriptions ──────────────────────────────────────────────────
-
-export async function subscribeProject(projectId: number, rulebookId: number): Promise<void> {
-  await apiPost(`/api/projects/${projectId}/rulebook-subscriptions`, { rulebook_id: rulebookId });
-}
-
-export async function unsubscribeProject(projectId: number, rulebookId: number): Promise<void> {
-  return apiDelete(`/api/projects/${projectId}/rulebook-subscriptions/${rulebookId}`);
-}
+// ── A project's rules ──────────────────────────────────────────────
 
 export async function getProjectApplicableRules(projectId: number): Promise<ApplicableRules> {
   return apiGet(`/api/projects/${projectId}/rules`);
@@ -293,24 +269,6 @@ export async function createProjectRule(
   return apiPost(`/api/projects/${projectId}/rules`, data);
 }
 
-// ── Suppressions ───────────────────────────────────────────────────
-
-export async function suppressRuleForProject(projectId: number, ruleId: number): Promise<void> {
-  await apiPost(`/api/projects/${projectId}/suppressions/rules/${ruleId}`, {});
-}
-
-export async function unsuppressRuleForProject(projectId: number, ruleId: number): Promise<void> {
-  return apiDelete(`/api/projects/${projectId}/suppressions/rules/${ruleId}`);
-}
-
-export async function suppressTopicForProject(projectId: number, topicId: number): Promise<void> {
-  await apiPost(`/api/projects/${projectId}/suppressions/topics/${topicId}`, {});
-}
-
-export async function unsuppressTopicForProject(projectId: number, topicId: number): Promise<void> {
-  return apiDelete(`/api/projects/${projectId}/suppressions/topics/${topicId}`);
-}
-
 
 /**
  * One row of the staleness sweep. Unlike RuleHeader this carries the CHECK
@@ -337,9 +295,9 @@ export interface RuleVerificationRow {
  * first, never-checked at the top. Rules without a check never appear:
  * they are decisions, and there is nothing to go and check.
  *
- * Not filterable by project — a project reaches rules through project
- * scope, subscriptions, always-on rulebooks and exclusions, and a filter
- * missing one of those paths would under-report.
+ * Not filterable by project — a project is bound by its own rules and by
+ * every global rule, and a filter that dropped the global ones would
+ * under-report.
  */
 export async function listRulesDueForVerification(opts: {
   olderThanDays?: number;