v2.34.1 — page-switch serialization lock

Page-switch serialization — the concurrency primitive for safe multi-agent use.

• Added src/utils/page_lock.py — Resolve has a single globally-active page, so two agents that flip pages concurrently corrupt each other. page_lock() serializes page switches: a reentrant intra-process lock plus a best-effort inter-process advisory file lock around the outermost section. The open_page action now routes through it. Required before any concurrent-agent feature ships.

Networked transport, sandboxed scripting, and capability/role scoping (the rest of the safe remote/multi-user design) are security-critical and remain a separate, sign-off-gated phase — intentionally not shipped here. Live-validated on DaVinci Resolve Studio 21.0.0.