Added CRDT snapshotting

server/migrations/20260629000000_crdt_snapshot.sql

@@ -0,0 +1,9 @@
+-- Stores a serialized CRDT state snapshot so startup can skip replaying
+-- the full op log.  Only the single most recent snapshot row is kept.
+CREATE TABLE IF NOT EXISTS crdt_snapshot (
+    id          INTEGER PRIMARY KEY CHECK (id = 1),
+    at_seq      INTEGER NOT NULL,
+    max_rowid   INTEGER NOT NULL,
+    state_json  TEXT    NOT NULL,
+    created_at  TEXT    NOT NULL
+);