[Bug]: randId() uses Math.random() — collision risk across devices and messages

[danditomaso]

apps/web/src/core/utils/randId.ts:2 generates IDs with Math.floor(Math.random() * 1e9) — ~30 bits of entropy, no crypto guarantees. Used for device IDs and other identifiers where collisions cause silent state corruption.

Switch to crypto.getRandomValues() or crypto.randomUUID().