feat(ECR-023): AICoreConfig KnowledgeSource 只读并 Closed

运营可观测知识源目录（knowledge_sources + admin /ai），不含 Chunk/Embedding。

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/migrations/000024_knowledge_sources.down.sql

@@ -0,0 +1,2 @@
+-- ECR-023 down
+DROP TABLE IF EXISTS knowledge_sources;

apps/api/migrations/000024_knowledge_sources.up.sql

@@ -0,0 +1,29 @@
+-- ECR-023 AICoreConfig KnowledgeSource (read catalog)
+
+CREATE TABLE IF NOT EXISTS knowledge_sources (
+  id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+  code varchar(64) NOT NULL UNIQUE,
+  title varchar(128) NOT NULL,
+  description text NULL,
+  source_kind varchar(32) NOT NULL
+    CHECK (source_kind IN ('faq', 'policy', 'guide')),
+  version int NOT NULL DEFAULT 1 CHECK (version > 0),
+  active boolean NOT NULL DEFAULT true,
+  system boolean NOT NULL DEFAULT false,
+  created_at timestamptz NOT NULL DEFAULT now(),
+  updated_at timestamptz NOT NULL DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS idx_knowledge_sources_active ON knowledge_sources(active);
+
+INSERT INTO knowledge_sources(code, title, description, source_kind, version, active, system)
+VALUES (
+  'ask_grounding',
+  '问答 grounding 知识源',
+  '运营可观测的 Ask grounding 目录占位；本切片不含 KnowledgeChunk。',
+  'faq',
+  1,
+  true,
+  true
+)
+ON CONFLICT (code) DO NOTHING;