Replace SpoolBuddy self-update with SSH-based updates from Bambuddy

The daemon's self-update mechanism (git fetch/reset on its own code) was
  fragile: .git permission errors, self-modifying code mid-run, hardcoded
  main branch. Bambuddy now SSHes into the SpoolBuddy Pi and drives the
  update remotely — matching its own branch, with step-by-step progress
  via WebSocket. Install script updated with SSH access, sudoers entry,
  and --ssh-pubkey flag for pairing.

frontend/src/api/client.ts

@@ -5035,6 +5035,9 @@ export const spoolbuddyApi = {
       body: '{}',
     }),
 
+  getSSHPublicKey: () =>
+    request<{ public_key: string }>('/spoolbuddy/ssh/public-key'),
+
   writeTag: (deviceId: string, spoolId: number) =>
     request<{ status: string }>('/spoolbuddy/nfc/write-tag', {
       method: 'POST',