api: pair the mobile app with device tokens

MB1 (spec 13). Decision 0005: our own Android/iPhone app, Expo in the
mobile repo, user portal only, no push in v1.

- mobile_devices (migration 0013): one-time pairing codes from My settings
  (QR or server + code, 10 minutes), traded by the app for an spm_ device
  token that acts as its user and never as an admin
- POST /api/me/mobile-devices/pair (web session only), POST /api/mobile/pair,
  GET/DELETE /api/me/mobile-devices
- signing out everywhere (password change or reset, disabling) removes
  paired phones too
- My settings: Mobile app section with the QR code and paired phones
- mobile/ (its own repo) ignored here

apps/api/src/db/migrations/meta/_journal.json

@@ -92,6 +92,13 @@
       "when": 1792951905226,
       "tag": "0012_sso",
       "breakpoints": true
+    },
+    {
+      "idx": 13,
+      "version": "7",
+      "when": 1793052019332,
+      "tag": "0013_mobile_devices",
+      "breakpoints": true
     }
   ]
 }