The CLI credentials upload stored claude_config.cli_credentials_file server-side,
but the path was then lost and CLI mode fell back to the OAuth2 credentials file:

- uploadClaudeCliFile() only showed a toast; unlike its sibling
  uploadFileChunked(), it never mirrored the stored path into providersData.
- saveProvider() posts providersData wholesale, and api_provider_save replaced
  the provider config outright, so a page loaded before the upload wiped the key
  on the next save.
- There was no field for cli_credentials_file — it appeared only in help text —
  so the value was invisible and unrecoverable once lost.

Preserve keys inside *_config blocks the client did not send, which fixes the
whole class rather than this one key: any server-set key would have been dropped
the same way. Only merges into a block the client actually sent, so a provider
type change still drops the old block and nothing is resurrected. A key the
client does send always wins, including falsy values like use_cli_mode=false.

Add the missing text field (admin only — DB users keep CLI credentials in
user_oauth2_credentials, not in claude_config), and mirror the upload result
into providersData. The chunk endpoint now also returns config_path, the tilde
form actually written to providers.json; file_path is absolute, so mirroring it
would post back a value that disagrees with what the server stored.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>