[v0.4.4] lock-recovery: detect and break stale file locks

[lora-sys]

Follow-up from v0.4.1 review.

Problem

withFileLock in packages/core/src/vault.mjs uses a lockfile (.lock). If the holding process is killed (SIGKILL, OOM, power loss), the lockfile is left behind. Subsequent writers time out (5s) and fail.

Goal

Detect stale locks (e.g., lock file older than 30s) and break them, with logging.

Scope

• packages/core/src/vault.mjs (withFileLock)
• Optional: emit a warning toast in the UI when a stale lock is broken

Acceptance Criteria

• Stale locks (older than threshold) are detected and broken automatically
• Warning is logged when this happens
• Tests cover the stale-lock scenario