Update docs for persistence support

CLAUDE.md

@@ -15,7 +15,6 @@ working:
 not yet:
 - cursor/selection sync (awareness protocol stubbed but unused)
 - other editor adapters (helix, kakoune, zed)
-- persistence (rooms are ephemeral)
 - reconnection handling
 
 ## stack
@@ -28,9 +27,10 @@ not yet:
 ## running
 
 ```bash
-just dev          # daemon on :4040
-bun test          # unit tests
-just check        # biome lint
+just dev                      # daemon on :4040
+COLLABD_DB=path.db just dev   # custom db path (default: collabd.db)
+bun test                      # unit tests
+just check                    # biome lint
 ```
 
 ## vim adapter usage
@@ -66,6 +66,7 @@ server -> client:
 - src/index.ts - websocket server, room routing
 - src/session.ts - yjs doc per room, peer management
 - src/protocol.ts - message types
+- src/db.ts - sqlite persistence, save/load crdt updates
 - adapters/vim/bridge.ts - bun process vim spawns
 - adapters/vim/collab.vim - vim9script plugin
 
@@ -95,7 +96,6 @@ known gaps (not production ready):
 - room names guessable via brute force
 - no encryption (deploy behind wss, not ws)
 - no audit logging
-- no persistence (data lost on daemon restart)
 
 before production:
 1. auth layer (jwt tokens or unix socket for local-only)