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

src/scribe/services/trash.py

@@ -83,22 +83,6 @@ async def _cascade(session, user_id: int, etype: str, eid: int, batch: str, now)
         await _set(session, Milestone, [Milestone.user_id == user_id, Milestone.project_id == eid], batch, now)
         # Project-scoped rules cascade with the project they're attached to.
         await _set(session, Rule, [Rule.project_id == eid], batch, now)
-        # Suppressions are pure associations (no deleted_at) — hard-delete
-        # them here so restoring the project doesn't bring stale mutes back.
-        # FK CASCADE would handle a full DELETE on the project row, but the
-        # soft-delete path keeps the project row alive; this guarantees the
-        # rows are gone whether or not the project ever gets purged.
-        from scribe.models.rulebook import (
-            project_rule_suppressions, project_topic_suppressions,
-        )
-        await session.execute(
-            sql_delete(project_rule_suppressions)
-            .where(project_rule_suppressions.c.project_id == eid)
-        )
-        await session.execute(
-            sql_delete(project_topic_suppressions)
-            .where(project_topic_suppressions.c.project_id == eid)
-        )
         await _set(session, Project, [Project.user_id == user_id, Project.id == eid], batch, now)
     elif etype == "milestone":
         await _set(session, Note, [Note.user_id == user_id, Note.milestone_id == eid], batch, now)