initial commit on Federted servers

db/migrations/004_bookmark_version.sql

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+-- 004_bookmark_version.sql — optimistic concurrency for bookmark updates
+-- (review CR-04). Owner-driven PUT /api/bookmarks/{id} (fields and tag
+-- replacement) now requires the expected version and bumps it; the
+-- column-deletion move bumps it too, so a client holding a stale snapshot
+-- gets a 409 instead of silently overwriting a concurrent edit. Sharing and
+-- server-driven flags (alertSent) stay outside the contract.
+ALTER TABLE "Bookmark" ADD COLUMN IF NOT EXISTS version integer NOT NULL DEFAULT 0;