[bug] Rename TinyBBS devices from the dashboard

[sayhiben]

Summary

• Add BBSClient.rename_device(preferred_name) and persist the server-assigned name returned by TinyBBS.
• Call the rename API from /settings when the BBS device name changes or the live client is out of sync.
• Keep the BBS rename reconciliation in a small helper so the settings route stays focused on form collection and persistence.
• Validate dashboard names before saving pending offline renames, using the same trim/length/character rules as the server.
• Save the final adjusted name when the server resolves duplicates, keep the previous BBS name on rename failure, and queue a pending rename when BBS is unavailable.
• Reconcile a pending dashboard name on the next BBS startup.
• Report old-server/non-JSON rename failures as clear HTTP errors.

Order

Depends on cuneytozseker/TinyProgrammerServerPublic#2. Merge and deploy the server PR first so /functions/v1/rename-device exists before this dashboard flow is used.

Fixes #45

Validation

• python3 -m py_compile main.py config.py bbs/client.py web/app.py web/config_manager.py
• Manual BBSClient.rename_device exercise with a local HTTP server, including non-JSON HTTP 404 handling.
• Manual Flask /settings exercises for live rename success, validation failure, pending rename without BBS, and out-of-sync live BBS state.
• Manual _apply_bbs_device_name_update helper exercise for success, failure, validation, and pending paths.
• Manual client/dashboard exercise against local Supabase: settings rename, bbs_client.device_name, saved token assigned_name, feed author, and restart persistence.