fix: scope sub_agent_skills unique constraint to tenant/project/agent (#2190)

* fix: scope sub_agent_skills unique constraint to tenant/project/agent

The unique constraint on sub_agent_skills was only on (sub_agent_id, skill_id),
causing cross-tenant collisions when different tenants use sub-agents with
the same ID and skill. Updated to include tenant_id, project_id, and agent_id.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* test: add cross-tenant regression test for sub_agent_skills unique constraint

Addresses review feedback: verifies different tenants can use the same
(sub_agent_id, skill_id) combination, and same-tenant duplicates are
still blocked.

Also fixes trailing newline in migration SQL.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: nick-inkeep

.changeset/cuddly-purple-fish.md

@@ -0,0 +1,5 @@
+---
+"@inkeep/agents-core": patch
+---
+
+Fix multi-tenant unique constraint on sub_agent_skills table to scope by tenant, project, and agent

packages/agents-core/drizzle/manage/0010_oval_angel.sql

@@ -0,0 +1,2 @@
+ALTER TABLE "sub_agent_skills" DROP CONSTRAINT "sub_agent_skills_sub_agent_skill_unique";--> statement-breakpoint
+ALTER TABLE "sub_agent_skills" ADD CONSTRAINT "sub_agent_skills_sub_agent_skill_unique" UNIQUE("tenant_id","project_id","agent_id","sub_agent_id","skill_id");