feat(providers): add Vercel AI Gateway and OpenRouter support (#902)

* add Vercel and OpenRouter as OpenAI-compatible LLM providers

* fix(fmt): fix cargo fmt line length issues in provider id tests

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* style(hermesllm): fix rustfmt formatting in provider id tests

* Add Vercel and OpenRouter to zero-config planoai up defaults

Wires `vercel/*` and `openrouter/*` into the synthesized default config so
`planoai up` with no user config exposes both providers out of the box
(env-keyed via AI_GATEWAY_API_KEY / OPENROUTER_API_KEY, pass-through
otherwise). Registers both in SUPPORTED_PROVIDERS_WITHOUT_BASE_URL so
wildcard model entries validate without an explicit provider_interface.

---------

Co-authored-by: Musa Malik <musam@uw.edu>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

cli/planoai/defaults.py

@@ -81,6 +81,21 @@ PROVIDER_DEFAULTS: list[ProviderDefault] = [
         base_url="https://inference.do-ai.run/v1",
         model_pattern="digitalocean/*",
     ),
+    ProviderDefault(
+        name="vercel",
+        env_var="AI_GATEWAY_API_KEY",
+        base_url="https://ai-gateway.vercel.sh/v1",
+        model_pattern="vercel/*",
+    ),
+    # OpenRouter is a first-class provider — the `openrouter/` model prefix is
+    # accepted by the schema and brightstaff's ProviderId parser, so no
+    # provider_interface override is needed.
+    ProviderDefault(
+        name="openrouter",
+        env_var="OPENROUTER_API_KEY",
+        base_url="https://openrouter.ai/api/v1",
+        model_pattern="openrouter/*",
+    ),
 ]