Add Get Started on Hex section to README

ClickHouse Cloud blocks port 9000 (plaintext native protocol), only
accepting connections on port 9440 (native + TLS). Users connecting
via DataStore hit NO_REMOTE_SHARD_AVAILABLE because the default is
remote() on port 9000.

Mirror the auto-detection logic from clickhouse-client (PRs #56638,
#56649, #74212):
- .clickhouse.cloud hosts -> secure=True + default port 9440
- Port 9440 on any host -> secure=True
- Support ?secure=true in clickhouse:// URIs

Separate the single `using-chdb` skill into two focused skills to match
distinct user mental models: pandas-style DataStore vs raw ClickHouse SQL.

- chdb-datastore: drop-in pandas replacement with decision tree, connectors
  reference, API reference, 11 examples, and verify_install.py
- chdb-sql: in-process SQL with table functions, SQL functions references,
  9 examples, and verify_install.py
- Rewrite install_skill.sh: two-skill install, --project flag, interactive
  agent selection, .agents/ path support
- Update README.md AI Coding Agent Skills section

…-secure

Auto-detect ClickHouse Cloud secure connections

Split agent skill into chdb-datastore and chdb-sql