chore: rename quicproquo → quicprochat in Rust workspace

Rename all crate directories, package names, binary names, proto
package/module paths, ALPN strings, env var prefixes, config filenames,
mDNS service names, and plugin ABI symbols from quicproquo/qpq to
quicprochat/qpc.

crates/quicprochat-sdk/src/lib.rs

@@ -0,0 +1,20 @@
+//! Client SDK for quicprochat v2.
+//!
+//! Provides `QpqClient` — a single entry point for connecting, authenticating,
+//! sending/receiving messages, and subscribing to real-time events.
+
+pub mod auth;
+pub mod client;
+pub mod config;
+pub mod conversation;
+pub mod devices;
+pub mod error;
+pub mod events;
+pub mod groups;
+pub mod keys;
+pub mod messaging;
+pub mod outbox;
+pub mod recovery;
+pub mod state;
+pub mod transcript;
+pub mod users;