Fix worktree creation and archive flow

Server: drop the synchronous branch-name generator dep, use the
worktree slug as the initial branch, and move first-agent branch
auto-naming to an async post-creation step backed by a structured
LLM call. Guards against renaming when the placeholder branch has
already been changed.

App: make workspace and worktree archive optimistic, rolling back
the local hide if the daemon call fails, and suppress incoming
workspace upserts while an archive is pending.

packages/server/package.json

@@ -74,6 +74,7 @@
     "dotenv": "^17.2.3",
     "express": "^4.18.2",
     "fast-deep-equal": "^3.1.3",
+    "mnemonic-id": "^3.2.7",
     "node-pty": "1.2.0-beta.11",
     "onnxruntime-node": "^1.23.0",
     "openai": "^4.20.0",