mobile: network member management and avatars (parity phase 2)

- New NetworkSettingsScreen (reachable from the stream-list header) lists
  members with admin remove, an invite-by-email sheet, and pending
  invitations with revoke — backed by new use-member-management hooks.
- Avatars: add avatar_object_id to HumanSchema, uploadAvatar/deleteAvatar/
  getAvatarDownloadUrl client methods (raw PUT via expo-file-system), a
  use-avatar-url hook, and image rendering in the shared Avatar component.
  AccountScreen gains a tap-to-change profile picture via expo-image-picker.
- auth-store gains refreshUser to pick up avatar changes.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01LqGPzXQ1AA9CqYHgCgmbtV

js/mobile/package.json

@@ -31,6 +31,7 @@
     "expo-device": "~8.0.10",
     "expo-file-system": "~19.0.16",
     "expo-haptics": "~15.0.7",
+    "expo-image-picker": "~17.0.8",
     "expo-notifications": "~0.32.17",
     "expo-secure-store": "~15.0.8",
     "expo-status-bar": "~3.0.9",