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-proto/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name        = "quicproquo-proto"
+version     = "0.1.0"
+edition     = "2021"
+description = "Cap'n Proto schemas, generated types, and serialisation helpers for quicproquo. No crypto, no I/O."
+license     = "MIT"
+
+# build.rs invokes capnpc to generate Rust source from .capnp schemas.
+build       = "build.rs"
+
+[dependencies]
+capnp       = { workspace = true }
+
+[build-dependencies]
+capnpc      = { workspace = true }