*_config: Invalid JSON syntax will clobber the entire file

[buecking]

smi:hgt $ chat mcp list                                                                                      
Name    Type    Command/URL    Arguments/Token    Environment    Auto-Confirm
------  ------  -------------  -----------------  -------------  --------------
todo    stdio   uvx            mcp-todo
todo    stdio   uvx            mcp-todo

smi:hgt $ echo '{' >>  /home/hgt/.local/share/y-cli/mcp_config.jsonl

smi:hgt $ chat mcp list                                   

Error loading MCP configs: Extra data: line 1 column 7 (char 6)
Error loading MCP configs: Extra data: line 1 column 7 (char 6)
Name    Type    Command/URL    Arguments/Token    Environment    Auto-Confirm
------  ------  -------------  -----------------  -------------  --------------
todo    stdio   uvx            mcp-todo

smi:hgt $ # ^ my config is empty