feat: Implement AI Router for Dynamic Agent Selection (#15227)

Adds intelligent routing system that automatically selects the best
agent for user queries based on conversation context.

### Changes:
- Added `routerModel` column to workspace table for configurable router
LLM selection
- Implemented `RouterService` with conversation history analysis and
agent matching logic
- Created router settings UI in AI Settings page with model dropdown
- Removed agent-specific thread associations - threads are now
agent-agnostic
- Added real-time routing status notification in chat UI with shimmer
effect
- Removed automatic default assistant agent creation
- Renamed GraphQL operations from agent-specific to generic (e.g.,
`agentChatThreads` → `chatThreads`)

---------

Co-authored-by: Félix Malfait <felix.malfait@gmail.com>
Co-authored-by: Félix Malfait <felix@twenty.com>

packages/twenty-front/src/modules/users/components/UserAndViewsProviderEffect.tsx

@@ -118,8 +118,6 @@ export const UserAndViewsProviderEffect = () => {
         ...userQueryData.currentUser.currentWorkspace,
         defaultRole:
           userQueryData.currentUser.currentWorkspace.defaultRole ?? null,
-        defaultAgent:
-          userQueryData.currentUser.currentWorkspace.defaultAgent ?? null,
       });
     }