Self-hosted: chat_advanced overrides all model selection, sidebar picker and chat_default are ignored

Problem

On self-hosted Khoj (v1.42.10, billing disabled), chat_advanced is used for ALL LLM calls — intent classification, code generation, title generation, and chat responses. The sidebar model picker and chat_default server setting have no effect.

Root Cause

In database/adapters/__init__.py, ais_user_subscribed() returns True when state.billing_enabled is False (line 422). This means all self-hosted users are treated as "subscribed."

In aget_default_chat_model(), for subscribed users with fast=True:

1. think_paid_fast — checked first, but these columns don't exist yet in v1.42.10 schema (migration not shipped), so always None
2. think_paid_deep — same, always None
3. chat_advanced — this is what gets returned for every call

chat_default is only reached in the else (non-subscribed) branch at line 1345, which never executes on self-hosted.

Impact

1. Sidebar model picker is ignored — UserConversationConfig.setting_id is never checked because chat_advanced takes priority
2. chat_default is dead config — never used on self-hosted
3. Intent classification uses the same model as chat — no way to use a fast/cheap model for tool selection and a different model for responses
4. Agent chat_model assignment is ignored for the default agent — get_agent_chat_model returns dynamically resolved model which hits the same chat_advanced path

Verified With

• LangFuse traces showing all 4 steps (intent, code gen, chat, title) use chat_advanced model regardless of sidebar selection
• Tested changing chat_default, sidebar model picker, agent model — all ignored
• Only changing chat_advanced in the database affects which model is used

Environment

• Khoj v1.42.10 (ghcr.io/khoj-ai/khoj:latest)
• Self-hosted, billing disabled
• PostgreSQL backend
• LiteLLM as OpenAI-compatible proxy

Suggested Fix

For self-hosted (billing disabled), either:

1. Don't treat all users as "subscribed" — or add a separate flag for self-hosted
2. Make chat_default work as the fast/intent model regardless of subscription status
3. Respect the sidebar model picker for the chat response step even when server settings are configured