feat: unread message tracking with blue dot indicator

Add ContactThreadRead model to track when users last viewed each contact thread.
Contacts with messages newer than the last read time show a blue dot in the sidebar.
Opening a thread automatically marks it as read via markThreadRead mutation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/graphql/generated.ts

@@ -87,8 +87,11 @@ export type Contact = {
   avatar: Scalars['String']['output'];
   channels: Array<Scalars['String']['output']>;
   description: Scalars['String']['output'];
+  hasUnread: Scalars['Boolean']['output'];
   id: Scalars['ID']['output'];
   lastContactAt: Scalars['String']['output'];
+  lastMessageChannel: Scalars['String']['output'];
+  lastMessageText: Scalars['String']['output'];
   name: Scalars['String']['output'];
 };
 
@@ -220,6 +223,7 @@ export type Mutation = {
   logPilotNote: MutationResult;
   login: MutationResult;
   logout: MutationResult;
+  markThreadRead: MutationResult;
   rollbackChangeSetItems: MutationResult;
   rollbackLatestChangeSet: MutationResult;
   selectChatConversation: MutationResult;
@@ -277,6 +281,11 @@ export type MutationloginArgs = {
 };
 
 
+export type MutationmarkThreadReadArgs = {
+  contactId: Scalars['ID']['input'];
+};
+
+
 export type MutationrollbackChangeSetItemsArgs = {
   changeSetId: Scalars['ID']['input'];
   itemIds: Array<Scalars['ID']['input']>;
@@ -464,7 +473,7 @@ export type ContactInboxesQueryQuery = { __typename?: 'Query', contactInboxes: A
 export type ContactsQueryQueryVariables = Exact<{ [key: string]: never; }>;
 
 
-export type ContactsQueryQuery = { __typename?: 'Query', contacts: Array<{ __typename?: 'Contact', id: string, name: string, avatar: string, channels: Array<string>, lastContactAt: string, description: string }> };
+export type ContactsQueryQuery = { __typename?: 'Query', contacts: Array<{ __typename?: 'Contact', id: string, name: string, avatar: string, channels: Array<string>, lastContactAt: string, lastMessageText: string, lastMessageChannel: string, hasUnread: boolean, description: string }> };
 
 export type CreateCalendarEventMutationMutationVariables = Exact<{
   input: CreateCalendarEventInput;
@@ -544,6 +553,13 @@ export type LogoutMutationMutationVariables = Exact<{ [key: string]: never; }>;
 
 export type LogoutMutationMutation = { __typename?: 'Mutation', logout: { __typename?: 'MutationResult', ok: boolean } };
 
+export type MarkThreadReadMutationVariables = Exact<{
+  contactId: Scalars['ID']['input'];
+}>;
+
+
+export type MarkThreadReadMutation = { __typename?: 'Mutation', markThreadRead: { __typename?: 'MutationResult', ok: boolean } };
+
 export type MeQueryQueryVariables = Exact<{ [key: string]: never; }>;
 
 
@@ -921,6 +937,9 @@ export const ContactsQueryDocument = gql`
     avatar
     channels
     lastContactAt
+    lastMessageText
+    lastMessageChannel
+    hasUnread
     description
   }
 }
@@ -1399,6 +1418,35 @@ export function useLogoutMutationMutation(options: VueApolloComposable.UseMutati
   return VueApolloComposable.useMutation<LogoutMutationMutation, LogoutMutationMutationVariables>(LogoutMutationDocument, options);
 }
 export type LogoutMutationMutationCompositionFunctionResult = VueApolloComposable.UseMutationReturn<LogoutMutationMutation, LogoutMutationMutationVariables>;
+export const MarkThreadReadDocument = gql`
+    mutation MarkThreadRead($contactId: ID!) {
+  markThreadRead(contactId: $contactId) {
+    ok
+  }
+}
+    `;
+
+/**
+ * __useMarkThreadReadMutation__
+ *
+ * To run a mutation, you first call `useMarkThreadReadMutation` within a Vue component and pass it any options that fit your needs.
+ * When your component renders, `useMarkThreadReadMutation` returns an object that includes:
+ * - A mutate function that you can call at any time to execute the mutation
+ * - Several other properties: https://v4.apollo.vuejs.org/api/use-mutation.html#return
+ *
+ * @param options that will be passed into the mutation, supported options are listed on: https://v4.apollo.vuejs.org/guide-composable/mutation.html#options;
+ *
+ * @example
+ * const { mutate, loading, error, onDone } = useMarkThreadReadMutation({
+ *   variables: {
+ *     contactId: // value for 'contactId'
+ *   },
+ * });
+ */
+export function useMarkThreadReadMutation(options: VueApolloComposable.UseMutationOptions<MarkThreadReadMutation, MarkThreadReadMutationVariables> | ReactiveFunction<VueApolloComposable.UseMutationOptions<MarkThreadReadMutation, MarkThreadReadMutationVariables>> = {}) {
+  return VueApolloComposable.useMutation<MarkThreadReadMutation, MarkThreadReadMutationVariables>(MarkThreadReadDocument, options);
+}
+export type MarkThreadReadMutationCompositionFunctionResult = VueApolloComposable.UseMutationReturn<MarkThreadReadMutation, MarkThreadReadMutationVariables>;
 export const MeQueryDocument = gql`
     query MeQuery {
   me {