fix: suppress verbose coglet logs during cog predict (#2722)
The Go CLI sets COG_LOG_LEVEL=warning by default (debug with --debug),
but coglet was reading COG_LOG instead, so the setting was ignored.
- Rename COG_LOG to COG_LOG_LEVEL in coglet Rust code to match the CLI
- Configure Python logging from COG_LOG_LEVEL in the server entry point
- Demote "Starting Rust coglet server" to debug level
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
