feat(shared-triggers): shared column on triggers (M2.1)

A group-owned trigger marked `shared = true` watches a §11.6 shared
collection instead of per-app collections — the namespace boundary that lets
a shared-collection write fire a trigger. Mirrors the sealed column; existing
rows default false (per-app, unchanged). Match-query split + emission land in
M2.2/M2.3.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/manager-core/migrations/0061_shared_triggers.sql

@@ -0,0 +1,21 @@
+-- §11.6 / §4.5: SHARED-collection triggers.
+--
+-- A §11.6 shared collection is group-owned and written by any subtree app via
+-- the `kv::shared_collection(...)` handles. Until now such writes fired NO
+-- trigger (the "group trigger has no app to watch" deferral): the per-app
+-- trigger dispatch keys on the writer app's OWN collections, and a shared
+-- collection lives in a distinct group-keyed store.
+--
+-- A SHARED trigger closes that gap: a group-owned trigger template marked
+-- `shared = true` watches the group's shared collection (not per-app
+-- collections). On a shared-collection write the emitter matches these triggers
+-- by the OWNING GROUP's chain and runs the handler under the WRITER app
+-- (`cx.app_id`) — the same "group template runs under the firing app" model.
+--
+-- The `shared` marker is the namespace boundary: a `shared = false` trigger
+-- (the default, incl. every existing row) watches per-app collections exactly
+-- as before; a `shared = true` trigger watches shared collections only. The two
+-- never cross (the per-app match queries add `AND t.shared = FALSE`, the shared
+-- match queries `AND t.shared = TRUE`).
+
+ALTER TABLE triggers ADD COLUMN shared BOOLEAN NOT NULL DEFAULT FALSE;

crates/manager-core/tests/expected_schema.txt

@@ -409,6 +409,7 @@ table: triggers
   name: text NOT NULL default=(gen_random_uuid())::text
   group_id: uuid NULL
   sealed: boolean NOT NULL default=false
+  shared: boolean NOT NULL default=false
 
 table: vars
   id: uuid NOT NULL default=gen_random_uuid()
@@ -940,3 +941,4 @@ constraints on vars:
   0058: template suppressions
   0059: sealed templates
   0060: group suppressions
+  0061: shared triggers