moq-lite-05: add broadcast Epoch and rename ANNOUNCE messages (#35)

Add an Epoch field to ANNOUNCE_BROADCAST (a varint, before the Hop ID
list): an opaque, application-defined value ordering instances of a
broadcast, where larger means newer. It is origin-assigned and forwarded
unchanged by relays. Subscribers resolve duplicate advertisements of the
same broadcast by largest Epoch first (path length only breaks ties), so
a reconnecting publisher can take over immediately instead of waiting for
the stale session to time out.

Rename ANNOUNCE_INTEREST to ANNOUNCE_REQUEST (the subscriber's request to
receive announcements) and ANNOUNCE to ANNOUNCE_BROADCAST (the publisher's
per-broadcast advertisement); ANNOUNCE_OK is unchanged.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: kixelated