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-server/src/domain/devices.rs

@@ -0,0 +1,76 @@
+//! Device registry domain logic — register, list, revoke devices.
+
+use std::sync::Arc;
+
+use crate::storage::Store;
+
+use super::types::*;
+
+const MAX_DEVICES_PER_IDENTITY: usize = 5;
+
+/// Domain service for multi-device management.
+pub struct DeviceService {
+    pub store: Arc<dyn Store>,
+}
+
+impl DeviceService {
+    pub fn register_device(
+        &self,
+        req: RegisterDeviceReq,
+        caller_identity_key: &[u8],
+    ) -> Result<RegisterDeviceResp, DomainError> {
+        if req.device_id.is_empty() {
+            return Err(DomainError::BadParams(
+                "device_id must not be empty".into(),
+            ));
+        }
+
+        let count = self.store.device_count(caller_identity_key)?;
+        if count >= MAX_DEVICES_PER_IDENTITY {
+            return Err(DomainError::DeviceLimit(MAX_DEVICES_PER_IDENTITY));
+        }
+
+        let success =
+            self.store
+                .register_device(caller_identity_key, &req.device_id, &req.device_name)?;
+
+        Ok(RegisterDeviceResp { success })
+    }
+
+    pub fn list_devices(
+        &self,
+        caller_identity_key: &[u8],
+    ) -> Result<ListDevicesResp, DomainError> {
+        let raw = self.store.list_devices(caller_identity_key)?;
+        let devices = raw
+            .into_iter()
+            .map(|(device_id, device_name, registered_at)| DeviceInfo {
+                device_id,
+                device_name,
+                registered_at,
+            })
+            .collect();
+        Ok(ListDevicesResp { devices })
+    }
+
+    pub fn revoke_device(
+        &self,
+        req: RevokeDeviceReq,
+        caller_identity_key: &[u8],
+    ) -> Result<RevokeDeviceResp, DomainError> {
+        if req.device_id.is_empty() {
+            return Err(DomainError::BadParams(
+                "device_id must not be empty".into(),
+            ));
+        }
+
+        let success = self
+            .store
+            .revoke_device(caller_identity_key, &req.device_id)?;
+        if !success {
+            return Err(DomainError::DeviceNotFound);
+        }
+
+        Ok(RevokeDeviceResp { success })
+    }
+}