Model Selection: Update GPT-5 controls

[Ayush8923]

Is your feature request related to a problem?
GPT-5 family models have been added, but they don't support temperature or max_num_results, leading to confusion in the UI. This inconsistency impacts user experience when selecting models.

Describe the solution you'd like
Enhance the prompt editor with the following changes:

• Add new models: GPT-5.4, GPT-5.4 Pro, GPT-5.4 Mini, GPT-5.4 Nano, GPT-5, GPT-5 Mini, GPT-5 Nano, GPT-4.1
• Hide temperature slider and max results input when a gpt-5* model is selected
• Maintain visibility of these controls for non-GPT-5 models
• Ensure API payload for GPT-5 configs excludes temperature and max_num_results
• Centralize model additions/removals to only require editing app/lib/models.ts

Original issue

Describe the current behavior
Added GPT-5 family models (GPT-5, GPT-5 mini/nano, GPT-5.4, GPT-5.4 pro/mini/nano) and GPT-4.1 to the prompt editor. GPT-5 models don't support temperature or max_num_results, so these are hidden from the UI and excluded from the API payload when a GPT-5 model is selected.

Also centralized MODEL_OPTIONS which was duplicated across 3 files.

Describe the enhancement you'd like

New models added

• GPT-5.4, GPT-5.4 Pro, GPT-5.4 Mini, GPT-5.4 Nano

• GPT-5, GPT-5 Mini, GPT-5 Nano

• GPT-4.1

• Selecting any gpt-5* model hides temperature slider and max results input

• Selecting any non-GPT-5 model shows them as before

• API payload for GPT-5 configs omits temperature and max_num_results

• Adding/removing models now requires editing only app/lib/models.ts