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-server/src/federation/address.rs

@@ -0,0 +1,78 @@
+//! Parse `username@domain` federated addresses.
+//!
+//! A bare `username` (no `@`) is treated as local.
+
+/// A parsed federated address.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FederatedAddress {
+    pub username: String,
+    pub domain: Option<String>,
+}
+
+impl FederatedAddress {
+    /// Parse a `user@domain` string. Bare `user` → domain is `None`.
+    pub fn parse(input: &str) -> Self {
+        // Split on the *last* '@' so usernames can contain '@' in theory.
+        match input.rsplit_once('@') {
+            Some((user, domain)) if !domain.is_empty() && !user.is_empty() => Self {
+                username: user.to_string(),
+                domain: Some(domain.to_string()),
+            },
+            _ => Self {
+                username: input.to_string(),
+                domain: None,
+            },
+        }
+    }
+
+    /// Returns true if this address refers to a local user (no domain or domain matches local).
+    pub fn is_local(&self, local_domain: &str) -> bool {
+        match &self.domain {
+            None => true,
+            Some(d) => d == local_domain,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn bare_username() {
+        let addr = FederatedAddress::parse("alice");
+        assert_eq!(addr.username, "alice");
+        assert_eq!(addr.domain, None);
+        assert!(addr.is_local("example.com"));
+    }
+
+    #[test]
+    fn user_at_domain() {
+        let addr = FederatedAddress::parse("alice@remote.example.com");
+        assert_eq!(addr.username, "alice");
+        assert_eq!(addr.domain, Some("remote.example.com".into()));
+        assert!(!addr.is_local("local.example.com"));
+        assert!(addr.is_local("remote.example.com"));
+    }
+
+    #[test]
+    fn trailing_at_is_bare() {
+        let addr = FederatedAddress::parse("alice@");
+        assert_eq!(addr.username, "alice@");
+        assert_eq!(addr.domain, None);
+    }
+
+    #[test]
+    fn leading_at_is_bare() {
+        let addr = FederatedAddress::parse("@domain.com");
+        assert_eq!(addr.username, "@domain.com");
+        assert_eq!(addr.domain, None);
+    }
+
+    #[test]
+    fn multiple_at_uses_last() {
+        let addr = FederatedAddress::parse("user@org@domain.com");
+        assert_eq!(addr.username, "user@org");
+        assert_eq!(addr.domain, Some("domain.com".into()));
+    }
+}