[ROADMAP][1.7] Make LLM configs fully configurable with system prompts and citation settings

[MODSetter]

Feature Description

Enhance the LLM configuration system to allow users to:

• Configure custom system prompts per LLM config
• Set citation behavior as default but make it configurable
• Create specialized configs for different use cases
• Share configs across search spaces

Target Deployment

• SurfSense Cloud (hosted version)
• Self-hosted version

Problem Statement

Current LLM config system:

• Has limited customization options
• Doesn't allow custom system prompts
• Has fixed citation behavior
• Cannot be easily tailored for specific use cases

Users need flexibility to create configs for:

• Research assistant (detailed, citation-heavy)
• Quick Q&A (concise, fast)
• Creative writing (flexible, no citations)
• Code assistant (technical, precise)

UI Enhancements

• Config Editor: Rich editor for system prompts
• Preset Library: Built-in presets for common use cases
• Config Sharing: Ability to share configs within teams
• Preview Mode: Test prompts before saving

Default Presets

• Research Assistant: Citations enabled, detailed responses
• Quick Q&A: Concise mode, minimal citations
• Code Helper: Technical focus, code formatting
• Creative: No citations, flexible format

Benefits

• Highly customizable AI behavior
• Users can tailor responses to their needs
• Better separation of concerns for different tasks
• Foundation for config marketplace/sharing

Use Case Examples

• User creates "Academic Research" config with specific citation format
• Team shares a "Customer Support" config optimized for their domain
• User switches between "Deep Research" and "Quick Answer" modes

Implementation Considerations

[x] This may require frontend changes (config editor UI)
[x] This may require backend changes (schema updates, prompt handling)
[x] This may require database changes (new config fields)
[x] This may affect existing features (existing configs need migration)

Files Likely Affected

• surfsense_backend/app/schemas/ - Config schemas
• surfsense_backend/app/services/ - Config service
• surfsense_backend/app/prompts/ - Prompt templates
• surfsense_web/components/settings/ - Config UI
• surfsense_web/hooks/use-llm-configs.ts - Config hooks

Acceptance Criteria

[ ] Config schema supports new fields
[ ] System prompts are properly applied to agent
[ ] Citation settings are respected
[ ] UI allows full config customization
[ ] Built-in presets are available
[ ] Existing configs migrated gracefully
[ ] Config validation prevents invalid settings

Migration Strategy

• Add new fields with sensible defaults
• Existing configs get enable_citations: true as default
• System prompts default to current behavior
• No breaking changes for existing users

Related Issues

• Blocks: Issue 1.8 (Deep agent chat interface)