docs(protocol): rewrite network protocol spec to match implementation

[lukyrys]

Rewrites LISH_NETWORK_PROTOCOL.md so it describes the protocol as actually implemented.

• the old text described a Kademlia DHT, WebRTC connections and JSON command messages, none of which exist in the code
• documents the real two-plane design: JSON control messages on per-network gossipsub topics (want, searchLishs, peer-announce) and the /lish/0.0.1 stream protocol with length-prefixed MessagePack messages (getLishs, getLish, getChunk, announceHave, searchResult)
• chunk identity is specified as the chunk checksum from the manifest (not a positional index), including how duplicate-content chunks share one identifier
• adds peer-visible limits and behavior: message signing, payload caps, rate limits, dedup windows, response timeouts, error codes and downloader peer penalties
• the synchronized LISH database (with optional incremental fetch from the last known LISH ID) and network access control stay in the spec as clearly marked planned extensions