feat: add Copilot connection diagnostics

Add backend support for Copilot connection and account-status UX without introducing raw provider credential management.

This change extends sidecar capabilities with explicit connection diagnostics, adds a refreshable capabilities IPC path, classifies common Copilot CLI failure modes, and includes a frontend handover document describing the new payload and expected UI states.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/KopayaAppService.ts

@@ -54,11 +54,11 @@ export class KopayaAppService extends EventEmitter<AppServiceEvents> {
   private sidecarCapabilities?: SidecarCapabilities;
 
   async describeSidecarCapabilities(): Promise<SidecarCapabilities> {
-    if (!this.sidecarCapabilities) {
-      this.sidecarCapabilities = await this.sidecar.describeCapabilities();
-    }
+    return this.loadSidecarCapabilities();
+  }
 
-    return this.sidecarCapabilities;
+  async refreshSidecarCapabilities(): Promise<SidecarCapabilities> {
+    return this.loadSidecarCapabilities(true);
   }
 
   async loadWorkspace(): Promise<WorkspaceState> {
@@ -494,4 +494,12 @@ export class KopayaAppService extends EventEmitter<AppServiceEvents> {
   private emitSessionEvent(event: SessionEventRecord): void {
     this.emit('session-event', event);
   }
+
+  private async loadSidecarCapabilities(forceRefresh = false): Promise<SidecarCapabilities> {
+    if (forceRefresh || !this.sidecarCapabilities) {
+      this.sidecarCapabilities = await this.sidecar.describeCapabilities();
+    }
+
+    return this.sidecarCapabilities;
+  }
 }

src/main/ipc/registerIpcHandlers.ts

@@ -12,6 +12,7 @@ import { KopayaAppService } from '@main/KopayaAppService';
 
 export function registerIpcHandlers(window: BrowserWindow, service: KopayaAppService): void {
   ipcMain.handle(ipcChannels.describeSidecarCapabilities, () => service.describeSidecarCapabilities());
+  ipcMain.handle(ipcChannels.refreshSidecarCapabilities, () => service.refreshSidecarCapabilities());
   ipcMain.handle(ipcChannels.loadWorkspace, () => service.loadWorkspace());
   ipcMain.handle(ipcChannels.addProject, () => service.addProject());
   ipcMain.handle(ipcChannels.removeProject, (_event, projectId: string) => service.removeProject(projectId));