feat: add API Route provider preset

[DennyHo0917]

Summary

Add API Route as an optional aggregator in the existing provider catalog. Users can save their key, fetch their accessible models, and import those model IDs through the existing OpenAI Chat Completions path.

• Base URL: https://global.api-route.com/v1.
• Authenticated model discovery; IDs are used unchanged without a vendor prefix.
• English and Chinese setup instructions.
• Extend the brand fallback inventory and add three setup/discovery flow tests.

Disclosure: I maintain API Route. This contribution was prepared and verified with Codex.

Validation

• Typecheck: pass.
• ESLint: pass (four existing warnings outside the changed files).
• Production build: pass.
• Focused preset/provider/discovery tests: 176 passed.
• Full suite on native Windows: 7,005 passed, 70 failed, 139 skipped. Failures include symlink EPERM, POSIX permission and shell expectations, and a renderer timeout; this is not a green full-suite result.
• Anonymous /v1/models: 401; a nonexistent path under /v1: 404.
• Live discovery using the repository's modelListRequest and parseModelList: 63 models, including gpt-6.1-sol.
• Live streaming chat using the repository's encodeOpenAIChat, SseParser and decodeOpenAIChat: API_ROUTE_OK.

Local environment limitation: npm ci installed dependencies but its Electron native rebuild step failed because the Windows C++ toolchain lacks Spectre-mitigated libraries. Typechecking, tests and bundling subsequently ran; I have not represented a native desktop launch as verified.