feat: use human-readable log format for local CLI commands
Coglet defaults to JSON structured logs for production (GKE/Stackdriver
compatibility), but this makes local development output hard to read.
Set LOG_FORMAT=console in cog serve, cog run, cog predict, and cog train
so developers see human-readable logs locally. Production is unaffected
since the env var is only set by the CLI for local commands.
