refactor: provider and selection strategy

[woorui]

What this PR does

This PR refactors provider management by introducing a unified provider registry shared by both Chat Completions and Model API routes.

Previously, provider selection logic was split between llm_provider and model_api_provider. This change consolidates selection, endpoint capability checks, and provider construction into a single provider_registry module.

Key changes

• Added a new unified registry: src/provider_registry.rs

  • Centralizes provider catalog building and endpoint-aware model selection.
  • Introduces endpoint-scoped selection via EndpointKind.
  • Supports custom chat/endpoint provider builders through extension hooks.
  • Preserves provider error notification wrapping.

• Removed duplicated registries/selection modules:

  • src/llm_provider/registry.rs
  • src/llm_provider/selection.rs
  • src/model_api_provider/registry.rs
  • src/model_api_provider/selection.rs

• Updated API layers to use the unified registry:

  • src/llm_api.rs now calls select_chat(...).
  • src/model_api.rs now calls select_endpoint(...).
  • Selection error handling now returns endpoint-specific messages:
    • model is required for /v1/...
    • model <x> is not supported for /v1/...

• Unified /v1/models source:

  • src/model_list.rs now reads from one registry instead of merging two registries.

• Simplified server boot wiring:

  • src/bin/yomo.rs now initializes one registry and shares it across:
    • LLM API
    • Model API
    • Model List API

Config and behavior updates

• ServeConfig has been simplified and unified:

  • Replaces separate llm_providers + llm_default_model_id + model_api.*
  • Uses:
    • providers: Vec<ProviderConfig>
    • endpoints: Vec<EndpointConfig>

• Added shared endpoint abstraction in serve_config:

  • EndpointKind
  • parse_generate_content_model(...)
  • endpoint path validation and parsing

• Provider type routing is now endpoint-capability driven.

  • Endpoint clients no longer enforce legacy endpoint-specific provider type names like "messages", "responses", "passthrough".
  • anthropic-messages / bedrock-messages naming is used consistently.

Tests

Added/updated unit tests for:

• endpoint-default selection behavior
• custom builder integration
• unsupported provider type rejection per endpoint
• duplicate endpoint path rejection
• endpoint capability enforcement
• model list filtering to endpoint-enabled models
• endpoint-aware selection error message formatting

[codecov]

Codecov Report

❌ Patch coverage is 67.02002% with 280 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.12%. Comparing base (a4168f2) to head (330ce99).

Files with missing lines	Patch %	Lines
src/provider_registry.rs	77.01%	157 Missing ⚠️
src/serve_config.rs	20.73%	65 Missing ⚠️
src/bin/yomo.rs	0.00%	24 Missing ⚠️
src/llm_api.rs	42.42%	19 Missing ⚠️
src/model_api.rs	50.00%	12 Missing ⚠️
src/model_list.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1264      +/-   ##
==========================================
+ Coverage   63.63%   65.12%   +1.48%     
==========================================
  Files          49       47       -2     
  Lines       12326    12400      +74     
==========================================
+ Hits         7844     8075     +231     
+ Misses       4482     4325     -157     

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[fanweixiao]

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