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/account.rs

@@ -0,0 +1,28 @@
+//! Account domain logic — account deletion with KT tombstone.
+
+use std::sync::{Arc, Mutex};
+
+use quicprochat_kt::MerkleLog;
+
+use crate::storage::Store;
+
+use super::types::DomainError;
+
+/// Domain service for account lifecycle operations.
+pub struct AccountService {
+    pub store: Arc<dyn Store>,
+    pub kt_log: Arc<Mutex<MerkleLog>>,
+}
+
+impl AccountService {
+    pub fn delete_account(&self, caller_identity_key: &[u8]) -> Result<(), DomainError> {
+        self.store.delete_account(caller_identity_key)?;
+
+        // Append a KT tombstone entry so the deletion is auditable.
+        if let Ok(mut log) = self.kt_log.lock() {
+            log.append("__tombstone__", caller_identity_key);
+        }
+
+        Ok(())
+    }
+}