Close frontend mutation-port and operation-vocabulary gaps for multiplayer wiring

## Problem

The current comfy-multi-player operation vocabulary covers add node, connect, set widget, delete node, and clear. Frontend graph behavior also includes geometry, groups, reroutes, node flags, single-link removal, subgraph edits, and undo. Those categories lack either a synchronized operation or a proven single frontend read/write port as multiplayer wiring begins.

## Goal

Ensure every multiplayer-relevant frontend mutation and read has one authoritative boundary and a representable synchronization operation.

## Proposed Solution

Inventory frontend ingress/egress against the multiplayer operation vocabulary, decide which categories are shared document state versus local view state, extend the vocabulary where required, and add round-trip/multi-client detectors.

## Acceptance Criteria

- Geometry, groups, reroutes, node flags, link removal, subgraphs, and undo are each classified.
- Every shared category has one authoritative frontend port and an operation/schema owner.
- Local-only view state is explicitly excluded with rationale.
- Multi-client tests cover every accepted shared operation.
- Remaining bypasses have bounded issues and owners.