fix: retain served model IDs in SGLang probes

[krunkosaurus]

SGLang can advertise a client-facing model ID through /v1/models while its native info endpoints report a filesystem path such as /model. The probe currently replaces the served ID with that path, so the dashboard loses the model name clients should use.

Preserve the normalized /v1/models ID after native SGLang enrichment, while retaining the native path in modelPath. Existing native fallback behavior remains available when no served ID is present. This brings an existing deployment fix forward to current main.

Validation:

• Both served-ID regressions fail against unchanged main, covering current native endpoints and deprecated endpoint fallback.
• SGLang suite: 28/28 pass.
• npm test: 318 server tests and 23 frontend tests pass.
• npm run typecheck, npm run build, and git diff --check pass.