Ship legacy migrate APIs, portfolio/blog old-id schema, and admin migrate/purge flows.

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

database/migrations/048_portfolios_author_id.sql

@@ -0,0 +1,20 @@
+-- Portfolio authors (same pattern as blogs.author_id)
+ALTER TABLE portfolios
+  ADD COLUMN IF NOT EXISTS author_id BIGINT;
+
+DO $$
+BEGIN
+  IF NOT EXISTS (
+    SELECT 1
+    FROM pg_constraint
+    WHERE conname = 'portfolios_author_id_fkey'
+  ) THEN
+    ALTER TABLE portfolios
+      ADD CONSTRAINT portfolios_author_id_fkey
+      FOREIGN KEY (author_id) REFERENCES users (id)
+      ON UPDATE NO ACTION
+      ON DELETE SET NULL;
+  END IF;
+END $$;
+
+CREATE INDEX IF NOT EXISTS idx_portfolios_author_id ON portfolios (author_id);