feat: Fix model attribution for prefix-stripped token usage callbacks

[AnishSarkar22]

Description

• Reconciles LiteLLM callback model names with registered model metadata when provider prefixes are stripped.
• Ensures token usage summaries preserve correct provider, display_name, model_id, and model_ref.
• Fixes incorrect model labels/icons in the message info menu caused by bare model-name collisions.
• Adds regression coverage for prefix-stripped model callbacks and exact metadata precedence.
• Integrates chat model selection handling in Composer and related components so selecting a model returns focus to the main composer input.
• Modified model selector chat models display logic.

Motivation and Context

FIX #

Screenshots

API Changes

• This PR includes API changes

Change Type

• Bug fix
• New feature
• Performance improvement
• Refactoring
• Documentation
• Dependency/Build system
• Breaking change
• Other (specify):

Testing Performed

• Tested locally
• Manual/QA verification

Checklist

• Follows project coding standards and conventions
• Documentation updated as needed
• Dependencies updated as needed
• No lint/build errors or new warnings
• All relevant tests are passing

High-level PR Summary

This PR fixes a model attribution bug where LiteLLM strips provider prefixes (e.g., azure/gpt-5.2-chat becomes gpt-5.2-chat) before invoking token tracking callbacks, causing incorrect model metadata to be displayed in the UI. The fix implements a dual-indexing system in TurnTokenAccumulator that reconciles both prefixed and bare model names with their metadata, preferring exact matches when available. Additionally, the PR improves UX by returning focus to the composer input after selecting a chat model and contains a minor metadata title change replacing en-dashes with hyphens.

⏱️ Estimated Review Time: 15-30 minutes

💡 Review Order Suggestion

Order	File Path
1	surfsense_backend/app/services/token_tracking_service.py
2	surfsense_backend/tests/unit/services/test_token_quota_service_cost.py
3	surfsense_web/components/new-chat/model-selector.tsx
4	surfsense_web/components/new-chat/chat-header.tsx
5	surfsense_web/components/assistant-ui/thread.tsx
6	surfsense_web/app/layout.tsx

⚠️ Inconsistent Changes Detected

File Path	Warning
surfsense_web/app/layout.tsx	Changing en-dashes to hyphens in metadata titles appears unrelated to the model attribution fix described in the PR

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