Fix config recovery hint and add config utils regression tests

[shuofengzhang]

What changed

• Updated read_configs() to load JSON via json.load() with explicit UTF-8 decoding.
• Fixed the broken-config guidance message to suggest hey config create (the actual command) instead of hey config init.
• Hardened init_config() to always create the config directory before writing config.json.
• Added regression tests for:
  • valid config loading,
  • invalid JSON fallback behavior,
  • error hint text including hey config create.

Why

• The previous recovery hint referenced a non-existent command (hey config init), which could mislead users during config repair.
• Ensuring directory creation inside init_config() makes config initialization robust even when called directly.
• New tests lock this behavior in and reduce risk of regressions.

Testing

• ✅ scripts/clone_and_test.sh lnxpy/hey (pass)