feat: add dataset checkpoint sync for MCP

migrations/004_dataset_versions.sql

@@ -0,0 +1,29 @@
+CREATE TABLE IF NOT EXISTS dataset_versions (
+  id SERIAL PRIMARY KEY,
+  hash VARCHAR(64) NOT NULL UNIQUE,
+  previous_hash VARCHAR(64),
+  crawl_run_id INTEGER REFERENCES crawl_runs(id),
+  employee_count INTEGER NOT NULL DEFAULT 0,
+  active_count INTEGER NOT NULL DEFAULT 0,
+  dismissed_count INTEGER NOT NULL DEFAULT 0,
+  created_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS ix_dataset_versions_created_at
+  ON dataset_versions (created_at);
+
+CREATE TABLE IF NOT EXISTS dataset_version_items (
+  id SERIAL PRIMARY KEY,
+  dataset_version_id INTEGER NOT NULL REFERENCES dataset_versions(id),
+  profile_key VARCHAR(255) NOT NULL,
+  employee_id INTEGER REFERENCES employees(id),
+  status VARCHAR(32) NOT NULL,
+  checksum VARCHAR(64) NOT NULL,
+  CONSTRAINT uq_dataset_version_items_version_profile UNIQUE (dataset_version_id, profile_key)
+);
+
+CREATE INDEX IF NOT EXISTS ix_dataset_version_items_hash
+  ON dataset_version_items (dataset_version_id);
+
+CREATE INDEX IF NOT EXISTS ix_dataset_version_items_profile_key
+  ON dataset_version_items (profile_key);