chore: rename project quicnprotochat -> quicproquo (binaries: qpq)

Rename the entire workspace:
- Crate packages: quicnprotochat-{core,proto,server,client,gui,p2p,mobile} -> quicproquo-*
- Binary names: quicnprotochat -> qpq, quicnprotochat-server -> qpq-server,
  quicnprotochat-gui -> qpq-gui
- Default files: *-state.bin -> qpq-state.bin, *-server.toml -> qpq-server.toml,
  *.db -> qpq.db
- Environment variable prefix: QUICNPROTOCHAT_* -> QPQ_*
- App identifier: chat.quicnproto.gui -> chat.quicproquo.gui
- Proto package: quicnprotochat.bench -> quicproquo.bench
- All documentation, Docker, CI, and script references updated

HKDF domain-separation strings and P2P ALPN remain unchanged for
backward compatibility with existing encrypted state and wire protocol.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

crates/quicproquo-core/proto/chat_message.proto

@@ -0,0 +1,21 @@
+syntax = "proto3";
+package quicproquo.bench;
+
+// Equivalent to the Envelope struct in delivery.capnp
+message Envelope {
+  uint64 seq = 1;
+  bytes data = 2;
+}
+
+// Equivalent to a chat message payload (app_message.rs Chat variant)
+message ChatMessage {
+  bytes message_id = 1;   // 16 bytes
+  string body = 2;        // UTF-8 text
+  uint64 timestamp_ms = 3;
+  bytes sender_key = 4;   // 32 bytes Ed25519 public key
+}
+
+// Batch fetch response (equivalent to fetch returning List(Envelope))
+message FetchResponse {
+  repeated Envelope payloads = 1;
+}