feat: Add support for saved model configurations

[irthomasthomas]

Implement persistent storage for OpenRouter model configurations using SQLite. This allows users to save specific combinations of model options (e.g., provider settings, online mode) under custom aliases for easy reuse.

Key changes:

• Introduce database functions (save_config, get_config, etc.) and schema for storing configurations.
• Add CLI commands openrouter save, openrouter list-saved, and openrouter remove-saved to manage saved aliases.
• Modify model registration to load saved configurations and register them as distinct models identifiable by their alias.
• Update model classes to apply saved options when building API requests, allowing prompt-specific options to override saved ones.

llm openrouter save openrouter/meta-llama/llama-4-scout \
    --name scout-groq-online \
    -o provider '{"order":["Groq"],"allow_fallbacks":true}' \
    -o online 1

To use:

llm -m scout-groq-online "what is the knowledge cutoff date of 'gemini-2.5'"

According to x.com, the training data cut off for Gemini 2.5 Pro is March 2025.

These can now be used in a consortium:

llm openrouter save openrouter/google/gemini-2.5-pro-preview-03-25 --name gemini-2.5-t0 -o provider '{                                                            
 "order": [
    "Google AI Studio"
  ],
"allow_fallbacks": false
}' -o temperature 0
llm openrouter save openrouter/google/gemini-2.5-pro-preview-03-25 --name gemini-2.5-t2 -o provider '{
  "order": [
    "Google AI Studio"
  ],
"allow_fallbacks": false
}' -o temperature 2

llm consortium save -m scout-groq-online -m gemini-2.5-t0 -m gemini-2.5-t2 \
--arbiter gemini-2.5-t0 \
groq-gemini-online

llm -m groq-gemini-online "Create a comprehensive UV cheatsheet. Highlight new UV features for 2024 and 2025 including a link to the announcement or docs."