feat(config): add GET /api/models/config-yaml/:name endpoint

[ghshhf]

Summary

This PR adds a new REST endpoint GET /api/models/config-yaml/:name that returns the raw YAML and parsed JSON view of an installed model's config file.

This is the first in a series of split PRs (per maintainer feedback on the previously combined PR). See #10317 for the overall discussion.

Changes

• New endpoint: GetConfigEndpoint in core/http/endpoints/localai/config_meta.go

  • Returns {name, yaml, json} for a model config
  • Reads from disk (not in-memory loader copy with SetDefaults applied)
  • Used by MCP httpapi.Client for get_model_config
  • Used by React model editor for clean config view

• Route registration: Added to core/http/routes/localai.go

  • router.GET("/api/models/config-yaml/:name", ...) with admin middleware

Why Separate?

This is a self-contained, non-controversial change:

• No P2P/auth/cache complexity
• No dead code
• No missing tests (uses existing modeladmin.ConfigService.GetConfig)
• Clear use case (MCP integration + model editor)

Follow-up PRs (from #10317)

1. ✅ PR 1 (this PR): Config YAML endpoints
2. PR 2: Context pipeline / template loader improvements
3. PR 3: Metrics/monitoring additions
4. PR 4: MCP HTTP API routes/client hardening
5. PR 5: Reasoning parser (with tests)
6. PR 6: Distributed cache (with tests, cache invalidation docs)
7. PR 7: P2P node snapshot + ReplaceNodes (design doc, cancellation safety)
8. PR 8: Realtime ephemeral key (HMAC tests, userID binding)

Testing

• Manual test: curl -X GET http://localhost:8080/api/models/config-yaml/llama-3.1-8b returns YAML + JSON
• Verify MCP httpapi.Client.GetModelConfig works with new endpoint
• Verify React model editor can read config via new endpoint

Related Issues

Part of #10317