Add setting to restrict model cycling (Ctrl+N) to custom models only

[Yoshuar]

Problem

When using customModels in ~/.factory/settings.json, pressing Ctrl+N cycles through all models (built-in + custom). Worse, custom models are not included in the cycle at all.

For users who exclusively use custom models (e.g. via a local proxy like CLIProxyAPI), cycling through built-in models is useless and disruptive.

Proposed Solution

Add a setting like modelCycleList or hideDefaultModels to settings.json:

{
  "hideDefaultModels": true
}

Or alternatively, a whitelist approach:

{
  "modelCycleList": [
    "custom:Claude-Opus-4.6-(Proxy)-0",
    "custom:Claude-Sonnet-4.5-(Proxy)-1"
  ]
}

This would make Ctrl+N only cycle through the specified/custom models.

Additional Context

Users running local proxies (BYOK) have no use for the built-in model list and would benefit from a cleaner, focused model selection experience.