feat(models): friendlier add-model form — OpenRouter/LM Studio, direct key, test & load

- Providers: add openrouter (https://openrouter.ai/api/v1) and lmstudio
  (http://localhost:1234/v1), both OpenAI-compatible. Selecting a provider now
  auto-fills its verified base URL, cost tier and default capabilities.
- API key is typed directly in the form and stored securely as a secret under the
  provider's env name — no manual env var to manage.
- New POST /admin/api/provider/models validates the key and lists the provider's
  models; a "Test & load models" button fills a searchable dropdown. The model
  field now sits below the key (some providers list models from the key).
- Fuller capability set: tools, vision, audio, reasoning, json, caching.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "cortiq-gateway"
-version = "0.2.9"
+version = "0.2.10"
 edition = "2021"
 rust-version = "1.75"
 license = "Apache-2.0"