feat: add documents table [D109] notion export storage with nested tree support

persona-brain-db/schema/16-documents.sql

@@ -0,0 +1,29 @@
+-- ============================================================
+-- 表16：documents（文档存储表）
+-- 用途：Notion导出存储，支持嵌套结构和树形路径
+-- 导入工作流：霜砚整理 → Notion API导出 → 写入本地documents表
+-- ============================================================
+
+CREATE TABLE IF NOT EXISTS documents (
+  document_id       VARCHAR(64)   PRIMARY KEY,
+  persona_id        VARCHAR(32)
+                    REFERENCES persona_identity(persona_id),
+  parent_id         VARCHAR(64)   REFERENCES documents(document_id),
+  path              TEXT          NOT NULL,        -- 树形路径，如 "/root/folder/doc"
+  title             VARCHAR(256)  NOT NULL,
+  content           TEXT,                          -- markdown内容
+  content_type      VARCHAR(32)   NOT NULL DEFAULT 'markdown'
+                    CHECK (content_type IN ('markdown', 'json', 'plain', 'notion')),
+  source            VARCHAR(32)   NOT NULL DEFAULT 'local'
+                    CHECK (source IN ('local', 'notion_import', 'api')),
+  tags              TEXT,                          -- JSON array
+  version           INTEGER       NOT NULL DEFAULT 1,
+  checksum          VARCHAR(64),
+  created_at        TIMESTAMP     NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  updated_at        TIMESTAMP     NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX IF NOT EXISTS idx_doc_persona ON documents(persona_id);
+CREATE INDEX IF NOT EXISTS idx_doc_parent ON documents(parent_id);
+CREATE INDEX IF NOT EXISTS idx_doc_path ON documents(path);
+CREATE INDEX IF NOT EXISTS idx_doc_source ON documents(source);