feat(ST-801): pg_notify triggers on tasks and stories

Add notify_task_change() and notify_story_change() PL/pgSQL functions
plus AFTER INSERT/UPDATE/DELETE triggers on tasks and stories. Each
write emits a JSONB payload on the 'scrum4me_changes' channel with
op, entity, id, product_id, sprint_id, assignee_id and (for UPDATE)
the list of changed columns. Tasks resolve product/sprint/assignee
via their parent story so the SSE handler can filter without an extra
DB roundtrip.

The migration is a side-effect-only change (no Prisma model/schema
diff) so the Prisma Client and TypeScript types are unaffected.

Verified locally with a node-pg LISTEN client: both task and story
mutations produce the expected payload within milliseconds.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

prisma/migrations/20260426230316_add_solo_realtime_triggers/migration.sql

@@ -0,0 +1,124 @@
+-- ST-801: Postgres LISTEN/NOTIFY infrastructure for realtime Solo Paneel.
+--
+-- Adds two row-level AFTER triggers that emit a JSON payload on the
+-- `scrum4me_changes` channel for every INSERT/UPDATE/DELETE on tasks and
+-- stories. The SSE handler at /api/realtime/solo subscribes to that channel
+-- and fans out per-user.
+--
+-- Payload shape:
+--   { op: 'I'|'U'|'D',
+--     entity: 'task'|'story',
+--     id: text,
+--     story_id?: text,        // task only
+--     product_id: text,
+--     sprint_id: text|null,
+--     assignee_id: text|null,
+--     changed_fields?: text[] // UPDATE only
+--   }
+--
+-- Channel name is hardcoded to keep the contract simple. Update both this
+-- migration and the SSE handler if it ever changes.
+
+CREATE OR REPLACE FUNCTION notify_task_change() RETURNS trigger AS $$
+DECLARE
+  rec record;
+  story_row record;
+  payload jsonb;
+BEGIN
+  IF TG_OP = 'DELETE' THEN
+    rec := OLD;
+  ELSE
+    rec := NEW;
+  END IF;
+
+  SELECT product_id, sprint_id, assignee_id
+    INTO story_row
+    FROM stories
+    WHERE id = rec.story_id;
+
+  IF NOT FOUND THEN
+    -- Parent story already gone (cascading delete); skip the notify.
+    RETURN rec;
+  END IF;
+
+  payload := jsonb_build_object(
+    'op', CASE TG_OP
+            WHEN 'INSERT' THEN 'I'
+            WHEN 'UPDATE' THEN 'U'
+            WHEN 'DELETE' THEN 'D'
+          END,
+    'entity', 'task',
+    'id', rec.id,
+    'story_id', rec.story_id,
+    'product_id', story_row.product_id,
+    'sprint_id', story_row.sprint_id,
+    'assignee_id', story_row.assignee_id
+  );
+
+  IF TG_OP = 'UPDATE' THEN
+    payload := payload || jsonb_build_object(
+      'changed_fields',
+      COALESCE((
+        SELECT jsonb_agg(n.key)
+        FROM jsonb_each(to_jsonb(NEW)) n
+        JOIN jsonb_each(to_jsonb(OLD)) o USING (key)
+        WHERE n.value IS DISTINCT FROM o.value
+      ), '[]'::jsonb)
+    );
+  END IF;
+
+  PERFORM pg_notify('scrum4me_changes', payload::text);
+  RETURN rec;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE OR REPLACE FUNCTION notify_story_change() RETURNS trigger AS $$
+DECLARE
+  rec record;
+  payload jsonb;
+BEGIN
+  IF TG_OP = 'DELETE' THEN
+    rec := OLD;
+  ELSE
+    rec := NEW;
+  END IF;
+
+  payload := jsonb_build_object(
+    'op', CASE TG_OP
+            WHEN 'INSERT' THEN 'I'
+            WHEN 'UPDATE' THEN 'U'
+            WHEN 'DELETE' THEN 'D'
+          END,
+    'entity', 'story',
+    'id', rec.id,
+    'product_id', rec.product_id,
+    'sprint_id', rec.sprint_id,
+    'assignee_id', rec.assignee_id
+  );
+
+  IF TG_OP = 'UPDATE' THEN
+    payload := payload || jsonb_build_object(
+      'changed_fields',
+      COALESCE((
+        SELECT jsonb_agg(n.key)
+        FROM jsonb_each(to_jsonb(NEW)) n
+        JOIN jsonb_each(to_jsonb(OLD)) o USING (key)
+        WHERE n.value IS DISTINCT FROM o.value
+      ), '[]'::jsonb)
+    );
+  END IF;
+
+  PERFORM pg_notify('scrum4me_changes', payload::text);
+  RETURN rec;
+END;
+$$ LANGUAGE plpgsql;
+
+DROP TRIGGER IF EXISTS tasks_notify_change ON tasks;
+CREATE TRIGGER tasks_notify_change
+  AFTER INSERT OR UPDATE OR DELETE ON tasks
+  FOR EACH ROW EXECUTE FUNCTION notify_task_change();
+
+DROP TRIGGER IF EXISTS stories_notify_change ON stories;
+CREATE TRIGGER stories_notify_change
+  AFTER INSERT OR UPDATE OR DELETE ON stories
+  FOR EACH ROW EXECUTE FUNCTION notify_story_change();