feat: add logging and error handling for wellknown config

[elithrar]

Adds debug logging and error handling for .well-known/opencode config fetches in enterprise installs.

Logs output both the config path (not present today) and a SHA-256 of the config so you can identify what version of the config is being pulled (or was, historically, when someone shares logs!) for a user.

Example log output with --print-logs:

DEBUG service=config url=https://opencode.example.com/.well-known/opencode fetching wellknown config
DEBUG service=config url=https://opencode.example.com/ hash=4142764bad628c8c8883665f9b17b4b32af24cb7ca9d4d4da57f85cc5ca21c18 loaded wellknown config