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/config.rs

@@ -0,0 +1,47 @@
+//! Client configuration.
+
+use std::net::SocketAddr;
+use std::path::PathBuf;
+
+/// Configuration for a `QpqClient` instance.
+#[derive(Debug, Clone)]
+pub struct ClientConfig {
+    /// Server address (host:port).
+    pub server_addr: SocketAddr,
+
+    /// Server hostname for TLS SNI.
+    pub server_name: String,
+
+    /// Path to the local conversation database.
+    pub db_path: PathBuf,
+
+    /// Password for encrypting the local database (SQLCipher).
+    /// If `None`, the database is stored unencrypted.
+    pub db_password: Option<String>,
+
+    /// Path to the local state file (identity key, MLS state).
+    pub state_path: PathBuf,
+
+    /// Whether to accept self-signed TLS certificates (dev mode only).
+    pub accept_invalid_certs: bool,
+
+    /// ALPN protocol identifier for the RPC service.
+    pub alpn: Vec<u8>,
+}
+
+impl Default for ClientConfig {
+    fn default() -> Self {
+        Self {
+            server_addr: std::net::SocketAddr::new(
+                std::net::IpAddr::V4(std::net::Ipv4Addr::new(127, 0, 0, 1)),
+                7000,
+            ),
+            server_name: "localhost".to_string(),
+            db_path: PathBuf::from("conversations.db"),
+            db_password: None,
+            state_path: PathBuf::from("client-state.bin"),
+            accept_invalid_certs: false,
+            alpn: b"qpc/2".to_vec(),
+        }
+    }
+}