refactor: remove Snowflake cloud scanning code — keep CoCo MCP only

[msaad00]

Problem

2,655 lines of Snowflake cloud scanning code is dormant:

• snowflake.py (1,756 lines) — account discovery, governance, activity
• snowflake_cis_benchmark.py (586 lines) — CIS checks
• snowflake_observability.py (313 lines) — query audit

We only use Snowflake for CoCo (Cortex Code CLI) MCP discovery, which works through discovery/config_parsers.py without any of this cloud code.

Action

• Remove snowflake.py, snowflake_cis_benchmark.py, snowflake_observability.py
• Remove --snowflake CLI flag and related options
• Keep CoCo MCP discovery in discovery/config_parsers.py (already works)
• Update tests, imports, docs
• Same treatment for Databricks cloud code if unused