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/routes/projects.py

@@ -99,8 +99,7 @@ async def create_project_route():
 @login_required
 async def decide_inception_route(project_id: int):
     """Record (or re-record) what a project inherits — milestone 297.
-    Body: the choices object {subscribe_rulebooks,
-    design_system_id, seed_systems}; owner-only."""
+    Body: the choices object {design_system_id, seed_systems}; owner-only."""
     uid = get_current_user_id()
     data = await request.get_json() or {}
     choices = data.get("choices", data)

src/scribe/routes/rulebooks.py

@@ -305,37 +305,7 @@ async def delete_rule(rule_id: int):
     return "", 204
 
 
-# ── Subscriptions ──────────────────────────────────────────────────────
-
-@rulebooks_bp.post("/projects/<int:project_id>/rulebook-subscriptions")
-@login_required
-async def subscribe_project(project_id: int):
-    data = await request.get_json() or {}
-    rulebook_id = data.get("rulebook_id")
-    if not rulebook_id:
-        return jsonify({"error": "rulebook_id is required"}), 400
-    try:
-        await rulebooks_svc.subscribe_project(
-            project_id=project_id, rulebook_id=int(rulebook_id), user_id=get_current_user_id(),
-        )
-    except ValueError as exc:
-        return jsonify({"error": str(exc)}), 404
-    return "", 204
-
-
-@rulebooks_bp.delete(
-    "/projects/<int:project_id>/rulebook-subscriptions/<int:rulebook_id>"
-)
-@login_required
-async def unsubscribe_project(project_id: int, rulebook_id: int):
-    try:
-        await rulebooks_svc.unsubscribe_project(
-            project_id=project_id, rulebook_id=rulebook_id, user_id=get_current_user_id(),
-        )
-    except ValueError as exc:
-        return jsonify({"error": str(exc)}), 404
-    return "", 204
-
+# ── A project's rule listing ───────────────────────────────────────────
 
 @rulebooks_bp.get("/projects/<int:project_id>/rules")
 @login_required
@@ -346,54 +316,6 @@ async def get_project_rules(project_id: int):
     return jsonify(result)
 
 
-@rulebooks_bp.post("/projects/<int:project_id>/suppressions/rules/<int:rule_id>")
-@login_required
-async def suppress_project_rule(project_id: int, rule_id: int):
-    try:
-        await rulebooks_svc.suppress_rule_for_project(
-            project_id=project_id, rule_id=rule_id, user_id=get_current_user_id(),
-        )
-    except ValueError as exc:
-        return jsonify({"error": str(exc)}), 404
-    return "", 204
-
-
-@rulebooks_bp.delete("/projects/<int:project_id>/suppressions/rules/<int:rule_id>")
-@login_required
-async def unsuppress_project_rule(project_id: int, rule_id: int):
-    try:
-        await rulebooks_svc.unsuppress_rule_for_project(
-            project_id=project_id, rule_id=rule_id, user_id=get_current_user_id(),
-        )
-    except ValueError as exc:
-        return jsonify({"error": str(exc)}), 404
-    return "", 204
-
-
-@rulebooks_bp.post("/projects/<int:project_id>/suppressions/topics/<int:topic_id>")
-@login_required
-async def suppress_project_topic(project_id: int, topic_id: int):
-    try:
-        await rulebooks_svc.suppress_topic_for_project(
-            project_id=project_id, topic_id=topic_id, user_id=get_current_user_id(),
-        )
-    except ValueError as exc:
-        return jsonify({"error": str(exc)}), 404
-    return "", 204
-
-
-@rulebooks_bp.delete("/projects/<int:project_id>/suppressions/topics/<int:topic_id>")
-@login_required
-async def unsuppress_project_topic(project_id: int, topic_id: int):
-    try:
-        await rulebooks_svc.unsuppress_topic_for_project(
-            project_id=project_id, topic_id=topic_id, user_id=get_current_user_id(),
-        )
-    except ValueError as exc:
-        return jsonify({"error": str(exc)}), 404
-    return "", 204
-
-
 @rulebooks_bp.post("/projects/<int:project_id>/rules")
 @login_required
 async def create_project_rule(project_id: int):