Make config load failures explicit and preserve defaults for missing config

[Copilot]

Config loading was silently swallowing parse failures, which made bad user config hard to diagnose as the config surface expanded. This change makes invalid config errors explicit while keeping missing config on the existing graceful-defaults path.

• Config load behavior

  • Change internal/config.Load / LoadFrom to return (Config, error).
  • Treat missing config file as a non-error and return defaults.
  • Surface invalid JSON and file read failures with contextual, user-facing errors.

• CLI error propagation

  • Update command entrypoints to handle config load errors instead of continuing with partially understood state.
  • Preserve normal startup behavior when no config file exists.

• Malformed config coverage

  • Extend config tests to distinguish:
    • missing file → defaults, no error
    • invalid JSON → defaults plus explicit error
    • valid file → loaded config, no error

Example of the new load contract:

cfg, err := config.LoadFrom(path)
if err != nil {
    return fmt.Errorf("invalid config: %w", err)
}

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.