config corruption

[mixmix]

We've see several instances of config corruption

• 🔥 entropy -a --help does not help and nukes config #244
• entropy fails to start with an empty config  #245
• Confusing error message when ENTROPY_TUI_ENDPOINT not set correctly, and failure to connect when setting the chain endpoint to localhost #268

It should not be possible, and if it happens (user or other program mutated config), then we should get more info.

To consider:

• atomic read/ write (lockfile?)
• write-lock in CLI code
• validation of input to config.set
  • is it an object?
  • does it have required fields?
    • JSON schema