refactor(errors): defer mutation errors to global handler

Now that MutationCache toasts via toUserMessage by default, the per-hook
onError duplicates drop away. Also normalizes inline query-error UI and
surfaces a previously-silent failure.

Mutations — removed redundant onError toasts:
- network-selector: useAcceptInvitation, createNetwork (inline)
- network-settings: useInviteMembers, useRevokeInvitation, useRemoveMember
- network-billing: useCreateCheckoutSession, useCreatePortalSession
  (onSuccess toasts stay — they carry domain context like network name)

Queries — consistent inline error UX via toUserMessage:
- network-selector: failed-to-load state gets a "Try again" button
- network-billing: "Couldn't load billing" includes friendly reason
- network-settings: useNetworkInvitations failure now surfaces a hint
  (previously rendered as "0 pending" — silently wrong)

Trimmed noisy JSDoc from PR 1 files (errors.ts, query-client.ts,
app-error-boundary.tsx, error-fallback.tsx, ipc-utils.ts).

js/src/main/ipc-utils.ts

@@ -6,9 +6,8 @@ type InvokeHandler = (
 ) => Promise<unknown> | unknown;
 
 /**
- * Wraps `ipcMain.handle` so handler failures log the full stack in the main
- * process and re-throw a sanitized message to the renderer. Without this,
- * main-process exceptions silently reject the renderer promise with no trace.
+ * Wraps `ipcMain.handle` so handler failures log with full stack in main and
+ * re-throw a sanitized message to the renderer.
  */
 export function safeHandle(channel: string, handler: InvokeHandler): void {
   ipcMain.handle(channel, async (event, ...args) => {