Scribe 2.3.4 - Update OpenAI Model options

Update AI model options to latest OpenAI models

What

• New models in the summary LLM selector — adds the GPT-5.6 family (gpt-5.6-sol, gpt-5.6-terra, gpt-5.6-luna) plus gpt-5.5, gpt-5.1, gpt-5, gpt-5-mini, and gpt-5-nano to the LLM_MODELS enum, which drives both the settings dropdown and the modal's model picker. Existing gpt-4.x entries are kept so previously saved selections still resolve.
• New default model — fresh installs now default to gpt-5.6-terra (OpenAI's recommended balanced tier). Existing users keep their saved setting.
• Temperature guard — GPT-5-family and o-series models reject any non-default temperature on the Chat Completions API (400 error). Summarization and mermaid-fix calls now only pass their hardcoded temperatures (0.5 / 0.3) to models that support it.
• Docs touch-up — custom chat model placeholder/example text updated from gpt-4o to gpt-5.6-terra.

Why

The selector topped out at gpt-4.1, several generations behind current OpenAI offerings. Without the temperature guard, simply adding the new models would have broken summarization with a 400 on every GPT-5-family request.

Testing

• npm run format:write and npm run build:prod (typecheck + build) pass cleanly.
• No settings migration needed: saved llmModel values remain valid enum members.

What's Changed

• Feat update model options for OpenAI model selection by @Mikodin in #107

Full Changelog: 2.3.3...2.3.4