feat: upgrade OpenMLS 0.5 → 0.8 for security patches and GREASE support

Migrates all MLS code in quicprochat-core from OpenMLS 0.5 to 0.8:
- StorageProvider replaces OpenMlsKeyStore (keystore.rs full rewrite)
- HybridCryptoProvider updated for new OpenMlsProvider trait
- Group operations updated for new API signatures
- MLS state persistence via MemoryStorage serialization
- tls_codec 0.3 → 0.4, openmls_traits/rust_crypto 0.2 → 0.5

crates/quicprochat-client/src/client/repl.rs

@@ -1449,10 +1449,8 @@ pub(crate) async fn cmd_dm(
         },
         display_name: format!("@{username}"),
         mls_group_blob: member
-            .group_ref()
-            .map(bincode::serialize)
-            .transpose()
-            .context("serialize group")?,
+            .serialize_mls_state()
+            .context("serialize MLS state")?,
         keystore_blob: None,
         member_keys,
         unread_count: 0,
@@ -1493,10 +1491,8 @@ pub(crate) fn cmd_create_group(session: &mut SessionState, name: &str) -> anyhow
         kind: ConversationKind::Group { name: name.to_string() },
         display_name: format!("#{name}"),
         mls_group_blob: member
-            .group_ref()
-            .map(bincode::serialize)
-            .transpose()
-            .context("serialize group")?,
+            .serialize_mls_state()
+            .context("serialize MLS state")?,
         keystore_blob: None,
         member_keys,
         unread_count: 0,
@@ -1780,9 +1776,7 @@ pub(crate) async fn cmd_join(
                     kind: ConversationKind::Group { name: display.clone() },
                     display_name: format!("#{display}"),
                     mls_group_blob: new_member
-                        .group_ref()
-                        .map(bincode::serialize)
-                        .transpose()
+                        .serialize_mls_state()
                         .context("serialize joined group")?,
                     keystore_blob: None,
                     member_keys,
@@ -3186,8 +3180,9 @@ async fn try_auto_join(
     };
 
     let mls_blob = member
-        .group_ref()
-        .and_then(|g| bincode::serialize(g).ok());
+        .serialize_mls_state()
+        .ok()
+        .flatten();
 
     let conv = Conversation {
         id: conv_id.clone(),