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

docs/api-keys-and-mcp.md

@@ -89,7 +89,7 @@ table here. The tools are grouped by family:
 | Projects / Milestones | `enter_project`, `get_project`, `create_milestone`, … | Containers and outcomes |
 | Search / Recall | `search`, `get_recent`, `list_tags`, `retrieval_telemetry` | Semantic + structured recall, and the readout its thresholds are tuned from |
 | Systems | `create_system`, `list_systems`, `list_system_records` | Reusable per-project subsystems/areas |
-| Rulebooks | `list_rules`, `create_rule`, `create_project_rule`, `subscribe_project_to_rulebook`, … | Engineering/workflow rules |
+| Rulebooks | `list_rules`, `create_rule`, `create_project_rule`, `relate_rules`, … | Engineering/workflow rules |
 | Processes | `list_processes`, `get_process`, `create_process` | Saved prompts/workflows |
 | Trash | `list_trash`, `restore`, `purge_trash` | Recoverable deletes |
 | Admin | `get_app_logs` (write/admin key) | Diagnostics |