chore: Fix provider configuration state

[fengju0213]

Summary

Fixes the provider configuration flow so a successfully validated BYOK/custom provider is saved, refreshed, and marked configured correctly.

Fixes #1665

Root Cause

The frontend sent is_valid, while the server model uses the existing is_vaild field. The server update allowlist also omitted endpoint_url, model_type, and encrypted_config, so updates could appear successful while leaving the stored provider unchanged. New providers could also fail to become the default immediately because the frontend read provider_id from stale React state.

Changes

• Send and read the provider validity state using the server-compatible is_vaild field, while still accepting is_valid for compatibility.
• Allow provider updates to persist endpoint_url, model_type, and encrypted_config.
• Use the freshly loaded provider id when setting a newly saved provider as default.
• Add server coverage for the is_valid compatibility input.

Impact

This affects all custom/BYOK providers, including AWS Bedrock and AWS Bedrock Converse. Direct AWS Bedrock users should still use the Bedrock Converse provider; the plain Bedrock provider remains for OpenAI-compatible Bedrock gateways.

Validation

• npm run type-check
• npx eslint src/pages/Agents/Models.tsx --no-warn-ignored --quiet
• uv run --extra dev pytest tests/test_provider_model.py
• uv run ruff check app/model/provider/provider.py app/domains/model_provider/service/provider_service.py tests/test_provider_model.py