Track per-employee chat read state and surface real unread counts

Adds chat_read_state migration (employee_id + space_id, last read
message + timestamp) wired through ChatService.markSpaceRead, IPC
markChatSpaceRead, and an effect in ChatPage that flushes the active
space whenever the latest message id changes.

Shell.computeBadges now derives the Messages badge from
(message.createdAt > read_state.last_read_at) minus messages the viewer
sent, so the sidebar shows true unread instead of total throughput.

AgentCompany-New/src/shared/commands.ts

@@ -89,6 +89,12 @@ export interface CreateChatSpaceInput {
   visibility: "workspace" | "restricted";
 }
 
+export interface MarkChatSpaceReadInput {
+  orgId: string;
+  employeeId: string;
+  spaceId: string;
+}
+
 export interface SaveProviderCredentialInput {
   orgId: string;
   providerId: string;

AgentCompany-New/src/shared/desktop-api.ts

@@ -8,6 +8,7 @@ import type {
   CreateApprovalInput,
   CreateChatSpaceInput,
   CreateMigrationReportInput,
+  MarkChatSpaceReadInput,
   CreateOrganizationInput,
   CreateProviderResponseInput,
   CreateScheduledPostInput,
@@ -40,6 +41,7 @@ export interface DesktopApi {
   decideApproval(input: DecideApprovalInput): Promise<DesktopResult<AppSnapshot>>;
   createChatSpace(input: CreateChatSpaceInput): Promise<DesktopResult<AppSnapshot>>;
   sendMessage(input: SendMessageInput): Promise<DesktopResult<AppSnapshot>>;
+  markChatSpaceRead(input: MarkChatSpaceReadInput): Promise<DesktopResult<AppSnapshot>>;
   saveProviderCredential(input: SaveProviderCredentialInput): Promise<DesktopResult<AppSnapshot>>;
   createProviderResponse(input: CreateProviderResponseInput): Promise<DesktopResult<AppSnapshot>>;
   importSkillDirectory(input: ImportSkillDirectoryInput): Promise<DesktopResult<AppSnapshot>>;

AgentCompany-New/src/shared/domain.ts

@@ -224,6 +224,14 @@ export interface ChatPresenceRecord {
   lastSeenAt: string;
 }
 
+export interface ChatReadStateRecord {
+  orgId: string;
+  employeeId: string;
+  spaceId: string;
+  lastReadMessageId: string | null;
+  lastReadAt: string;
+}
+
 export interface FileObjectRecord {
   id: string;
   orgId: string;
@@ -407,6 +415,7 @@ export interface AppSnapshot {
   chatThreads: ChatThreadRecord[];
   chatAttachments: ChatAttachmentRecord[];
   chatPresence: ChatPresenceRecord[];
+  chatReadStates: ChatReadStateRecord[];
   files: FileObjectRecord[];
   scheduledPosts: ScheduledPostRecord[];
   providers: ProviderRecord[];

AgentCompany-New/src/shared/ipc.ts

@@ -9,6 +9,7 @@ export const IPC_CHANNELS = {
   decideApproval: "agentcompany:decide-approval",
   createChatSpace: "agentcompany:create-chat-space",
   sendMessage: "agentcompany:send-message",
+  markChatSpaceRead: "agentcompany:mark-chat-space-read",
   saveProviderCredential: "agentcompany:save-provider-credential",
   createProviderResponse: "agentcompany:create-provider-response",
   importSkillDirectory: "agentcompany:import-skill-directory",