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>

schemas/federation.capnp

@@ -0,0 +1,54 @@
+# federation.capnp — Server-to-server federation RPC interface.
+#
+# Enables multiple quicproquo servers to relay messages across instances
+# via mutual TLS over QUIC. Each method carries a FederationAuth struct whose
+# `origin` field is validated against the mTLS certificate's SAN.
+#
+# ID generated with: capnp id
+@0xb7e3f4a1c9d82056;
+
+interface FederationService {
+  # Relay an enqueued payload to a recipient on this server.
+  relayEnqueue @0 (
+    recipientKey :Data,
+    payload      :Data,
+    channelId    :Data,
+    version      :UInt16,
+    auth         :FederationAuth
+  ) -> (seq :UInt64);
+
+  # Relay a batch enqueue to multiple recipients on this server.
+  relayBatchEnqueue @1 (
+    recipientKeys :List(Data),
+    payload       :Data,
+    channelId     :Data,
+    version       :UInt16,
+    auth          :FederationAuth
+  ) -> (seqs :List(UInt64));
+
+  # Fetch a KeyPackage for an identity hosted on this server.
+  proxyFetchKeyPackage @2 (
+    identityKey :Data,
+    auth        :FederationAuth
+  ) -> (package :Data);
+
+  # Fetch a hybrid public key for an identity hosted on this server.
+  proxyFetchHybridKey @3 (
+    identityKey :Data,
+    auth        :FederationAuth
+  ) -> (hybridPublicKey :Data);
+
+  # Resolve a username to identity key on this server.
+  proxyResolveUser @4 (
+    username :Text,
+    auth     :FederationAuth
+  ) -> (identityKey :Data);
+
+  # Health / readiness probe for the federation link.
+  federationHealth @5 () -> (status :Text, serverDomain :Text);
+}
+
+struct FederationAuth {
+  # Origin domain of the requesting server. Validated against mTLS cert SAN.
+  origin @0 :Text;
+}

schemas/node.capnp

@@ -1,4 +1,4 @@
-# node.capnp — Unified quicnprotochat node RPC interface.
+# node.capnp — Unified quicproquo node RPC interface.
 #
 # Combines Authentication and Delivery operations into a single service.
 #